Techniques for storing data

ABSTRACT

Described are techniques for storing data. A write operation is received that is directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address. The logical device has a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device. A storage tier is selected from a plurality of storage tiers from which to allocate storage for storing write data of the write operation. The selecting is performed in accordance with determining a match between an expected level of performance of the storage tier and the performance goal. First physical storage is allocated from the storage tier. A logical address subrange of the logical device is mapped to the first physical storage. The write data is stored in the first physical storage at a location mapped to the target logical address.

BACKGROUND Technical Field

This application generally relates to data storage and more particularly to techniques for storing data on physical storage devices.

Description of Related Art

Computer systems may include different resources used by one or more host processors. Resources and host processors in a computer system may be interconnected by one or more communication connections. These resources may include, for example, data storage devices such as those included in the data storage systems manufactured by EMC Corporation. These data storage systems may be coupled to one or more host processors and provide storage services to each host processor. Multiple data storage systems from one or more different vendors may be connected and may provide common data storage for one or more host processors in a computer system.

A host may perform a variety of data processing tasks and operations using the data storage system. For example, a host may perform basic system I/O (input/output) operations in connection with data requests, such as data read and write operations.

Host systems may store and retrieve data using a data storage system containing a plurality of host interface units, disk drives, and disk interface units. Such data storage systems are provided, for example, by EMC Corporation of Hopkinton, Mass. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the data storage system directly, but rather, access what appears to the host systems as a plurality of logical units, logical devices or logical volumes. The logical units may or may not correspond to the actual physical disk drives. Allowing multiple host systems to access the single data storage system allows the host systems to share data stored therein.

In connection with data storage, a variety of different technologies may be used. Data may be stored, for example, on different types of disk devices and/or flash memory devices. The data storage environment may define multiple storage tiers in which each tier includes physical devices or drives of varying technologies, performance characteristics, and the like. The physical devices of a data storage system, such as a data storage array, may be used to store data for multiple applications.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention is a method of storing data comprising: receiving a write operation directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address, the logical device having a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; selecting a storage tier from a plurality of storage tiers from which to allocate storage for storing write data of the write operation, wherein the selecting is performed in accordance with determining a match between an expected level of performance of the storage tier and the performance goal denoted by the service level objective; allocating first physical storage from the storage tier; mapping a logical address subrange of the logical device to the first physical storage; and storing the write data in the first physical storage at a physical storage location mapped to the target logical address. Each of the plurality of storage tiers may have a first characteristic denoting a media type of physical storage devices of said each tier and a second characteristic denoting a RAID type and configuration of physical storage devices. The media type associated with said each storage tier may denote an expected level of performance with respect to I/O operations directed to said each tier. The performance goal of the service level objective and the expected level of performance of the storage tier may be response times. The plurality of storage tiers may include a first storage tier having a first characteristic identifying a media type with an expected level of performance matching the performance goal of the service level objective and a second characteristic identifying a first RAID type and configuration, and a second storage tier having a first characteristic identifying a media type with an expected level of performance matching the performance goal of the service level objective and a second characteristic identifying a second RAID type and configuration. The selecting step may further comprise determining a first write penalty associated with the first RAID type and configuration; determining a second write penalty associated with the second RAID type and configuration; and selecting the first storage tier rather than the second storage tier from which to allocate storage for storing the write data if the first write penalty is less than the second write penalty, otherwise selecting the second storage tier rather than the first storage tier. The storage tier may be characterized by a first media type denoting that the storage tier includes physical devices of the first media type and wherein the storage tier is characterized by a first RAID type and configuration denoting that physical devices of the storage tier are configured into one or more RAID groups of the first RAID type and configuration. The method may further comprise collecting I/O workload information for a data portion including the target logical address and the logical address subrange of the logical device; determining, based on the I/O workload information, a preferred media type and a preferred RAID type and configuration for the data portion; determining, for first data of the data portion currently storage in the storage tier, whether the first RAID type and configuration matches the preferred RAID type and configuration, and whether the first media type matches the preferred media type; and responsive to determining that any of the first RAID type and configuration does not match the preferred RAID type and configuration, and the first media type does not match the preferred media type, selecting first data of the data portion to be moved from the storage tier to a target storage tier. The target storage tier may have the preferred RAID type and configuration and preferred media type. The I/O workload information may a write probability for the data portion. The I/O workload information may include an I/O density for the data portion. The I/O workload information may include a first metric based on I/O throughput for the data portion. The I/O workload information may include a second metric based on an amount of data read in connection with I/Os directed to the data portion and based on an amount of data written in connection with I/Os directed to the data portion.

In accordance with another aspect of the invention is a system comprising: a processor; and a memory comprising code stored therein that, when executed, performs a method comprising: receiving a write operation directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address, the logical device having a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; selecting a storage tier from a plurality of storage tiers from which to allocate storage for storing write data of the write operation, wherein the selecting is performed in accordance with determining a match between an expected level of performance of the storage tier and the performance goal denoted by the service level objective; allocating first physical storage from the storage tier; mapping a logical address subrange of the logical device to the first physical storage; and storing the write data in the first physical storage at a physical storage location mapped to the target logical address.

In accordance with another aspect of the invention is a computer readable medium comprising code stored thereon that, when executed, performs a method that stores data comprising: receiving a write operation directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address, the logical device having a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; selecting a storage tier from a plurality of storage tiers from which to allocate storage for storing write data of the write operation, wherein the selecting is performed in accordance with determining a match between an expected level of performance of the storage tier and the performance goal denoted by the service level objective; allocating first physical storage from the storage tier; mapping a logical address subrange of the logical device to the first physical storage; and storing the write data in the first physical storage at a physical storage location mapped to the target logical address. Each of the plurality of storage tiers may have a first characteristic denoting a media type of physical storage devices of said each tier and a second characteristic denoting a RAID type and configuration of physical storage devices. The media type associated with said each storage tier may denote an expected level of performance with respect to I/O operations directed to said each tier. The performance goal of the service level objective and the expected level of performance of the storage tier may be response times. The plurality of storage tiers may include a first storage tier having a first characteristic identifying a media type with an expected level of performance matching the performance goal of the service level objective and a second characteristic identifying a first RAID type and configuration, and a second storage tier having a first characteristic identifying a media type with an expected level of performance matching the performance goal of the service level objective and a second characteristic identifying a second RAID type and configuration, and wherein the selecting may further comprise determining a first write penalty associated with the first RAID type and configuration; determining a second write penalty associated with the second RAID type and configuration; and selecting the first storage tier rather than the second storage tier from which to allocate storage for storing the write data if the first write penalty is less than the second write penalty, otherwise selecting the second storage tier rather than the first storage tier. The storage tier may be characterized by a first media type denoting that the storage tier includes physical devices of the first media type and wherein the storage tier may be characterized by a first RAID type and configuration denoting that physical devices of the storage tier are configured into one or more RAID groups of the first RAID type and configuration, and the method may further comprise collecting I/O workload information for a data portion including the target logical address and the logical address subrange of the logical device; determining, based on the I/O workload information, a preferred media type and a preferred RAID type and configuration for the data portion; determining, for first data of the data portion currently storage in the storage tier, whether the first RAID type and configuration matches the preferred RAID type and configuration, and whether the first media type matches the preferred media type; and responsive to determining that any of the first RAID type and configuration does not match the preferred RAID type and configuration, and the first media type does not match the preferred media type, selecting first data of the data portion to be moved from the storage tier to a target storage tier. The target storage tier may have the preferred RAID type and configuration and the preferred media type. The I/O workload information may include a write probability for the data portion and an I/O density for the data portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 is an example of an embodiment of a system that may utilize the techniques described herein;

FIG. 2 is a representation of the logical internal communications between the directors and memory included in one embodiment of a data storage system of FIG. 1;

FIG. 3 is an example representing components that may be used in an embodiment in accordance with techniques herein;

FIGS. 4, 5A, 5B, 10, and 11 are examples illustrating a data storage system, such as data storage array, including a plurality of storage tiers in an embodiment in accordance with techniques herein;

FIG. 5C is a schematic diagram illustrating tables that are used to keep track of device information in connection with an embodiment of the system described herein;

FIG. 5D is a schematic diagram showing a group element of a thin device table in connection with an embodiment of the system described herein;

FIGS. 6, 7, 8, 9, 12, 13, 14, 15, 21, 22, 23 and 24 are flowcharts of processing steps that may be performed in an embodiment in accordance with techniques herein;

FIGS. 16A and 16B are examples illustrating thin devices and associated structures that may be used in an embodiment in accordance with techniques herein;

FIG. 16C is an example of how a thin device logical address range may be partitioned in an embodiment in accordance with techniques herein;

FIG. 17 is an example of tables of service plan levels, associated service level objectives (SLOs) and preferred media types that may be used in an embodiment in accordance with techniques herein;

FIG. 18 is an example of a default allocation ranking that may be used when initially allocating storage for a data portion, such as a thin device chunk, in an embodiment in accordance with techniques herein; and

FIGS. 19 and 20 are graphical illustrations of how preferred media type and preferred RAID type and configuration may be determined for a data portion in an embodiment in accordance with techniques herein.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Referring to FIG. 1, shown is an example of an embodiment of a system that may be used in connection with performing the techniques described herein. The system 10 includes a data storage system 12 connected to host systems 14 a-14 n through communication medium 18. In this embodiment of the computer system 10, and the n hosts 14 a-14 n may access the data storage system 12, for example, in performing input/output (I/O) operations or data requests. The communication medium 18 may be any one or more of a variety of networks or other type of communication connections as known to those skilled in the art. The communication medium 18 may be a network connection, bus, and/or other type of data link, such as a hardwire or other connections known in the art. For example, the communication medium 18 may be the Internet, an intranet, network (including a Storage Area Network (SAN)) or other wireless or other hardwired connection(s) by which the host systems 14 a-14 n may access and communicate with the data storage system 12, and may also communicate with other components included in the system 10.

Each of the host systems 14 a-14 n and the data storage system 12 included in the system 10 may be connected to the communication medium 18 by any one of a variety of connections as may be provided and supported in accordance with the type of communication medium 18. The processors included in the host computer systems 14 a-14 n may be any one of a variety of proprietary or commercially available single or multi-processor system, such as an Intel-based processor, or other type of commercially available processor able to support traffic in accordance with each particular embodiment and application.

It should be noted that the particular examples of the hardware and software that may be included in the data storage system 12 are described herein in more detail, and may vary with each particular embodiment. Each of the host computers 14 a-14 n and data storage system may all be located at the same physical site, or, alternatively, may also be located in different physical locations. Examples of the communication medium that may be used to provide the different types of connections between the host computer systems and the data storage system of the system 10 may use a variety of different communication protocols such as SCSI, Fibre Channel, iSCSI, and the like. Some or all of the connections by which the hosts and data storage system may be connected to the communication medium may pass through other communication devices, such switching equipment that may exist such as a phone line, a repeater, a multiplexer or even a satellite.

Each of the host computer systems may perform different types of data operations in accordance with different types of tasks. In the embodiment of FIG. 1, any one of the host computers 14 a-14 n may issue a data request to the data storage system 12 to perform a data operation. For example, an application executing on one of the host computers 14 a-14 n may perform a read or write operation resulting in one or more data requests to the data storage system 12.

It should be noted that although element 12 is illustrated as a single data storage system, such as a single data storage array, element 12 may also represent, for example, multiple data storage arrays alone, or in combination with, other data storage devices, systems, appliances, and/or components having suitable connectivity, such as in a SAN, in an embodiment using the techniques herein. It should also be noted that an embodiment may include data storage arrays or other components from one or more vendors. In subsequent examples illustrated the techniques herein, reference may be made to a single data storage array by a vendor, such as by EMC Corporation of Hopkinton, Mass. However, as will be appreciated by those skilled in the art, the techniques herein are applicable for use with other data storage arrays by other vendors and with other components than as described herein for purposes of example.

The data storage system 12 may be a data storage array including a plurality of data storage devices 16 a-16 n. The data storage devices 16 a-16 n may include one or more types of data storage devices such as, for example, one or more disk drives and/or one or more solid state drives (SSDs). An SSD is a data storage device that uses solid-state memory to store persistent data. An SSD using SRAM or DRAM, rather than flash memory, may also be referred to as a RAM drive. SSD may refer to solid state electronics devices as distinguished from electromechanical devices, such as hard drives, having moving parts. Flash devices or flash memory-based SSDs are one type of SSD that contains no moving parts. As described in more detail in following paragraphs, the techniques herein may be used in an embodiment in which one or more of the devices 16 a-16 n are flash drives or devices. More generally, the techniques herein may also be used with any type of SSD although following paragraphs may make reference to a particular type such as a flash device or flash memory device.

The data storage array may also include different types of adapters or directors, such as an HA 21 (host adapter), RA 40 (remote adapter), and/or device interface 23. Each of the adapters may be implemented using hardware including a processor with local memory with code stored thereon for execution in connection with performing different operations. The HAs may be used to manage communications and data operations between one or more host systems and the global memory (GM). In an embodiment, the HA may be a Fibre Channel Adapter (FA) or other adapter which facilitates host communication. The HA 21 may be characterized as a front end component of the data storage system which receives a request from the host. The data storage array may include one or more RAs that may be used, for example, to facilitate communications between data storage arrays. The data storage array may also include one or more device interfaces 23 for facilitating data transfers to/from the data storage devices 16 a-16 n. The data storage interfaces 23 may include device interface modules, for example, one or more disk adapters (DAs) (e.g., disk controllers), adapters used to interface with the flash drives, and the like. The DAs may also be characterized as back end components of the data storage system which interface with the physical data storage devices.

One or more internal logical communication paths may exist between the device interfaces 23, the RAs 40, the HAs 21, and the memory 26. An embodiment, for example, may use one or more internal busses and/or communication modules. For example, the global memory portion 25 b may be used to facilitate data transfers and other communications between the device interfaces, HAs and/or RAs in a data storage array. In one embodiment, the device interfaces 23 may perform data operations using a cache that may be included in the global memory 25 b, for example, when communicating with other device interfaces and other components of the data storage array. The other portion 25 a is that portion of memory that may be used in connection with other designations that may vary in accordance with each embodiment.

The particular data storage system as described in this embodiment, or a particular device thereof, such as a disk or particular aspects of a flash device, should not be construed as a limitation. Other types of commercially available data storage systems, as well as processors and hardware controlling access to these particular devices, may also be included in an embodiment.

Host systems provide data and access control information through channels to the storage systems, and the storage systems may also provide data to the host systems also through the channels. The host systems do not address the drives or devices 16 a-16 n of the storage systems directly, but rather access to data may be provided to one or more host systems from what the host systems view as a plurality of logical devices, logical volumes (LVs) which may also referred to herein as logical units (e.g., LUNs). A logical unit (LUN) may be characterized as a disk array or data storage system reference to an amount of disk space that has been formatted and allocated for use to one or more hosts. A logical unit may have a logical unit number that is an I/O address for the logical unit. As used herein, a LUN or LUNs may refer to the different logical units of storage which may be referenced by such logical unit numbers. The LUNs may or may not correspond to the actual or physical disk drives. For example, one or more LUNs may reside on a single physical disk drive, data of a single LUN may reside on multiple different physical devices, and the like. Data in a single data storage system, such as a single data storage array, may be accessed by multiple hosts allowing the hosts to share the data residing therein. The HAs may be used in connection with communications between a data storage array and a host system. The RAs may be used in facilitating communications between two data storage arrays. The DAs may be one type of device interface used in connection with facilitating data transfers to/from the associated disk drive(s) and LUN (s) residing thereon. A flash device interface may be another type of device interface used in connection with facilitating data transfers to/from the associated flash devices and LUN(s) residing thereon. It should be noted that an embodiment may use the same or a different device interface for one or more different types of devices than as described herein.

In an embodiment, the data storage system as described may be characterized as having one or more logical mapping layers in which a logical device of the data storage system is exposed to the host whereby the logical device is mapped by such mapping layers of the data storage system to one or more physical devices. Additionally, the host may also have one or more additional mapping layers so that, for example, a host side logical device or volume is mapped to one or more data storage system logical devices as presented to the host.

The device interface, such as a DA, performs I/O operations on a physical device or drive 16 a-16 n. In the following description, data residing on a LUN may be accessed by the device interface following a data request in connection with I/O operations that other directors originate or an I/O operation that is received from a host or other external client of the data storage system. For example, a host may issue an I/O operation which is received by the HA 21. The I/O operation may identify a target location from which data is read from, or written to, depending on whether the I/O operation is, respectively, a read or a write operation request. The target location of the received I/O operation may be expressed in terms of a LUN and logical address or offset location (e.g., LBA or logical block address) on the LUN. Processing may be performed on the data storage system to further map the target location of the received I/O operation, expressed in terms of a LUN and logical address or offset location on the LUN, to its corresponding physical device (PD) and location on the PD. The DA which services the particular PD may further perform processing to either read data from, or write data to, the corresponding physical device location for the I/O operation.

Also shown in FIG. 1 is a service processor 22 a that may be used to manage and monitor the system 12. In one embodiment, the service processor 22 a may be used in collecting performance data, for example, regarding the I/O performance in connection with data storage system 12. This performance data may relate to, for example, performance measurements in connection with a data request as may be made from the different host computer systems 14 a 14 n. This performance data may be gathered and stored in a storage area. Alternatively, an embodiment may provide for collection of such performance data using processor(s) and other components which are internal to the data storage system.

It should be noted that a service processor 22 a may exist external to the data storage system 12 and may communicate with the data storage system 12 using any one of a variety of communication connections. In one embodiment, the service processor 22 a may communicate with the data storage system 12 through three different connections, a serial port, a parallel port and using a network interface card, for example, with an Ethernet connection. Using the Ethernet connection, for example, a service processor may communicate directly with DAs and HAs within the data storage system 12.

It should be noted that each of the different adapters, such as HA 21, DA or disk interface, RA, and the like, may be implemented as a hardware component including, for example, one or more processors, one or more forms of memory, and the like. Code may be stored in one or more of the memories of the component for performing processing described herein in following paragraphs as well other suitable processing.

Referring to FIG. 2, shown is a representation of the logical internal communications between the directors and memory included in a data storage system. Included in FIG. 2 is a plurality of directors 37 a-37 n coupled to the memory 26. Each of the directors 37 a-37 n represents one of the HAs, RAs, or device interfaces that may be included in a data storage system. In an embodiment disclosed herein, there may be up to sixteen directors coupled to the memory 26. Other embodiments may allow a maximum number of directors other than sixteen as just described and the maximum number may vary with embodiment.

The representation of FIG. 2 also includes an optional communication module (CM) 38 that provides an alternative communication path between the directors 37 a-37 n. Each of the directors 37 a-37 n may be coupled to the CM 38 so that any one of the directors 37 a-37 n may send a message and/or data to any other one of the directors 37 a-37 n without needing to go through the memory 26. The CM 38 may be implemented using conventional MUX/router technology where a sending one of the directors 37 a-37 n provides an appropriate address to cause a message and/or data to be received by an intended receiving one of the directors 37 a-37 n. In addition, a sending one of the directors 37 a-37 n may be able to broadcast a message to all of the other directors 37 a-37 n at the same time.

With reference back to FIG. 1, components of the data storage system may communicate using GM 25 b. For example, in connection with a write operation, an embodiment may first store the data in cache included in a portion of GM 25 b, mark the cache slot including the write operation data as write pending (WP), and then later de-stage the WP data from cache to one of the devices 16 a-16 n. In connection with returning data to a host from one of the devices as part of a read operation, the data may be copied from the device by the appropriate device interface, such as a DA servicing the device. The device interface may copy the data read into a cache slot included in GM which is, in turn, communicated to the appropriate HA in communication with the host.

As described above, the data storage system 12 may be a data storage array including a plurality of data storage devices 16 a-16 n in which one or more of the devices 16 a-16 n are flash memory devices employing one or more different flash memory technologies. In one embodiment, the data storage system 12 may be a VMAX®data storage array by EMC Corporation of Hopkinton, Mass. In the foregoing data storage array, the data storage devices 16 a-16 n may include a combination of disk devices and flash devices in which the flash devices may appear as standard Fibre Channel (FC) drives to the various software tools used in connection with the data storage array. The flash devices may be constructed using nonvolatile semiconductor NAND flash memory. The flash devices may include one or more SLC (single level cell) devices and/or MLC (multi level cell) devices.

It should be noted that the techniques herein may be used in connection with flash devices comprising what may be characterized as enterprise-grade or enterprise-class flash drives (EFDs) with an expected lifetime (e.g., as measured in an amount of actual elapsed time such as a number of years, months, and/or days) based on a number of guaranteed write cycles, or program cycles, and a rate or frequency at which the writes are performed. Thus, a flash device may be expected to have a usage measured in calendar or wall clock elapsed time based on the amount of time it takes to perform the number of guaranteed write cycles. The techniques herein may also be used with other flash devices, more generally referred to as non-enterprise class flash devices, which, when performing writes at a same rate as for enterprise class drives, may have a lower expected lifetime based on a lower number of guaranteed write cycles.

The techniques herein may be generally used in connection with any type of flash device, or more generally, any SSD technology. The flash device may be, for example, a flash device which is a NAND gate flash device, NOR gate flash device, flash device that uses SLC or MLC technology, and the like, as known in the art. In one embodiment, the one or more flash devices may include MLC flash memory devices although an embodiment may utilize MLC, alone or in combination with, other types of flash memory devices or other suitable memory and data storage technologies. More generally, the techniques herein may be used in connection with other SSD technologies although particular flash memory technologies may be described herein for purposes of illustration.

An embodiment in accordance with techniques herein may have one or more defined storage tiers. Each tier may generally include physical storage devices or drives having one or more attributes associated with a definition for that tier. For example, one embodiment may provide a tier definition based on a set of one or more attributes. The attributes may include any one or more of a storage type or storage technology, a type of data protection, device performance characteristic(s), storage capacity, and the like. The storage type or technology may specify whether a physical storage device is an SSD drive (such as a flash drive), a particular type of SSD drive (such using flash or a form of RAM), a type of magnetic disk or other non-SSD drive (such as rotating disk drives of various speeds or RPMs (revolutions per minute) (e.g., 10K RPM, 15K RPM) using one or more interfaces such as FC, NL-SAS, SAS, SATA, etc.), and the like. Data protection may specify a type or level of data storage protection such, for example, as a particular RAID (redundant array of independent disks) level (e.g., RAID1, RAID-5 3+1, RAIDS 7+1, and the like). Performance characteristics may relate to different performance aspects of the physical storage devices of a particular type or technology. For example, there may be multiple types of FC rotating disk drives based on the RPM characteristics of the FC disk drives (e.g., 10K RPM FC drives and 15K RPM FC drives) and FC disk drives having different RPM characteristics may be included in different storage tiers. Storage capacity may specify the amount of data, such as in bytes, that may be stored on the drives. An embodiment may allow a user to define one or more such storage tiers. For example, an embodiment in accordance with techniques herein may define two storage tiers including a first tier of all SSD drives and a second tier of all non-SSD drives. As another example, an embodiment in accordance with techniques herein may define three storage tiers including a first tier of all SSD drives which are flash drives, a second tier of all FC 15K RPM drives, and a third tier of all SATA 7.2K RPM drives. The foregoing are some examples of tier definitions and other tier definitions may be specified in accordance with techniques herein.

Referring to FIG. 3, shown is an example 100 of components that may be used in an embodiment in connection with techniques herein. The example 100 includes performance data monitoring software 134 which gathers performance data about the data storage system. The software 134 may gather and store performance data 136. This performance data 136 may also serve as an input to other software, such as used in connection with performing data storage system optimizations, which attempt to enhance the performance of I/O operations, such as those I/O operations associated with data storage devices 16 a-16 n of the system 12 (as in FIG. 1). For example, the performance data 136 may be used by a data storage optimizer in an embodiment in accordance with techniques herein. The performance data 136 may be used in determining one or more statistics such, for example, a workload for one or more physical devices, a pool or group of physical devices, logical devices or volumes (e.g., LUNs), thin or virtually provisioned devices (described in more detail elsewhere herein), portions of thin devices, and the like. The workload may also be a measurement or level of “how busy” a device is, for example, in terms of I/O operations (e.g., I/O throughput such as number of I/Os/second, response time (RT), and the like). Examples of workload information and other information that may be obtained and used in an embodiment in accordance with techniques herein are described in more detail elsewhere herein.

It should be noted that additional details are described herein of processing that may be performed by the data storage optimizer 135. For example, the data storage optimizer 135 may perform data movements to physically move or relocate data portions between different storage tiers in a multi-tiered storage system in accordance with one or more criteria such as, for example, changing I/O workload information about different data portions. Data portions may be relocated between storage tiers responsive to changes in I/O workload information about the data portions over time.

In one embodiment, components of FIG. 3, such as the performance monitoring software, performance data 136 and/or data storage optimizer 135, may be located and execute on a system or processor that is external to the data storage system. For example, in one embodiment, any one or more of the foregoing components may be located and execute on service processor 22 a. As an alternative or in addition to having one or more components execute on a processor external to the data storage system, one or more of the foregoing components may be located and execute on a processor of the data storage system itself.

The response time (RT) for a logical or physical storage device or volume may be based on a response time associated with the logical or physical storage device or volume for a period of time. The response time may be based on read and write operations directed to the storage device or volume. Response time represents the amount of time it takes the storage system to complete an I/O request (e.g., a read or write request). Response time may be characterized as including two components: service time and wait time. Service time is the actual amount of time spent servicing or completing an I/O request after receiving the request from a host via an HA 21, or after the storage system 12 generates the I/O request internally. The wait time is the amount of time the I/O request spends waiting in line or queue waiting for service (e.g., prior to executing the I/O operation).

It should be noted that the operations of read and write with respect to a LUN, thin device, and the like, may be viewed as a front end I/O operation such as from the host or external client perspective which is translated into one or more corresponding backend or physical device I/O operations (e.g., read and write requests or commands from the DA 23, controller or other backend physical device interface to the physical storage device). Thus, the backend or physical device I/O operations (e.g., number of physical device reads, writes, and the like) are based on physical device accesses. The back end I/O operations may be contrasted with observing or counting a number of particular types of I/O requests (e.g., reads or writes) as issued from the host and received by a front end component such as an HA 21. To illustrate, a host read request may not result in a read request or command issued to the DA if there is a cache hit and the requested data is in cache. The host read request results in a read request or command issued to the DA 23 to retrieve data from the physical drive only if there is a read miss. Furthermore, when writing data of a received host I/O request to the physical device, the host write request may result in multiple reads and/or writes by the DA 23 in addition to writing out the host or user data of the request. For example, if the data storage system implements a RAID data protection technique, such as RAID-5, additional reads and writes may be performed such as in connection with reading other user data used to calculate parity information involving the new write data, and also writing out the new additional parity information for the user data. Thus, observed data or metrics such as related to I/O workload and I/O operations may be with respect to front end I/O operations, such as host I/O operations, and may also be related to back end or physical device I/O operations, such as back end or physical device I/O operations (e.g., the back-end read and write requests or commands performed by the DA). Such back end or physical device read and write commands may correspond, respectively, to physical device accesses such as disk reads and writes that may result from a host I/O request received by an HA 21.

In an example of an embodiment of a multi-tiered storage system, the techniques herein may be described with reference to a storage environment having three or more storage tiers. For example, an embodiment may have three storage tiers—a first tier of only SSD or flash drives in the data storage system, a second tier of only FC 15K RPM disk drives, and a third tier of only SATA 7.K RPMdisk drives. In terms of performance, the foregoing three tiers may be ranked from highest to lowest as follows: first, second, and then third. The lower the tier ranking, the lower the tier's performance characteristics (e.g., longer latency times, capable of less I/O throughput/second/GB (or other storage unit), and the like). Generally, different types of physical devices or physical drives have different types of characteristics. There are different reasons why one may want to use one storage tier and type of drive over another depending on criteria, goals and the current performance characteristics exhibited in connection with performing I/O operations. For example, flash drives of the first tier may be a best choice or candidate for storing data which may be characterized as I/O intensive or “busy” thereby experiencing a high rate of I/Os to frequently access the physical storage device containing the LUN's data. However, flash drives tend to be expensive in terms of storage capacity. SATA 7.2K RPM drives may be a best choice or candidate for storing data of devices requiring a large storage capacity and which are not I/O intensive with respect to access and retrieval from the physical storage device. The second tier of FC 15K RPM disk drives may be characterized as “in between” flash drives and SATA drives in terms of cost/GB and I/O performance. Thus, in terms of relative performance characteristics, flash drives may be characterized as having higher performance than both FC 15K RPM and SATA 7.2K RPM disks, and FC 15K RPM disks may be characterized as having a higher performance than SATA 7.2K RPM disks.

Since flash drives of the first tier are the best suited for high throughput/sec/GB, processing may be performed to determine which of the devices, and data portions thereof, are characterized as most I/O intensive and therefore may be good candidates to have their data stored on flash drives. Similarly, the second most I/O intensive devices, and portions thereof, may be good candidates to store on FC 15K RPM disk drives of the second tier and the least I/O intensive devices may be good candidates to store on SATA 7.2K RPM drives of the third tier. As such, workload for an application may be determined using some measure of I/O intensity, performance or activity (e.g., I/O throughput/second, percentage of read operation, percentage of write operations, response time, etc.) of each device used for the application's data. Some measure of workload may be used as a factor or criterion in combination with others described herein for determining what data portions are located on the physical storage devices of each of the different storage tiers. As described in more detail herein, other criterion/criteria may also be used in connection with selecting what data is stored on the particular storage tiers in a data storage system in an embodiment in accordance with techniques herein.

FIG. 4 is a schematic illustration showing a storage system 150 that may be used in connection with an embodiment of the system described herein. The storage system 150 may include a storage array 124 having multiple directors 130-132 and multiple storage volumes (logical devices, LUNs, or VOLUMES 0-3) 110-113. Host applications 140-144 and/or other entities (e.g., other storage devices, SAN switches, etc.) request data writes and data reads to and from the storage array 124 that are facilitated using one or more of the directors 130-132. The storage array 124 may include similar features as that discussed above.

The volumes 110-113 may be provided in multiple storage tiers (TIERS 0-3) that may have different storage characteristics, such as speed, cost, reliability, availability, security and/or other characteristics. As described above, a tier may represent a set of storage resources, such as physical storage devices, residing in a storage platform. Examples of storage disks that may be used as storage resources within a storage array of a tier may include sets SATA 7.2K RPM disks, FC 15K RPM disks and/or EFDs, among other known types of storage devices.

According to various embodiments, each of the volumes 110-113 (as well as data portions of a single volume) may be located in different storage tiers. Tiered storage provides that data may be initially allocated to a particular fast volume/tier, but a portion of the data that has not been used over a period of time may be automatically moved to a slower (and perhaps less expensive) tier. For example, data that is expected to be used frequently, for example database indices, may be initially written directly to fast storage whereas data that is not expected to be accessed frequently may be initially written to slower storage. In an embodiment, the system described herein may be used in connection with a Fully Automated Storage Tiering (FAST) product produced by EMC Corporation of Hopkinton, Mass., that provides for the optimization of the use of different storage tiers including the ability to easily create and apply tiering policies (e.g., allocation policies, data movement policies including promotion and demotion thresholds, and the like) to transparently automate the control, placement, and movement of data within a storage system based on business needs.

With reference back to FIG. 3, FAST is one example of a data storage optimizer 135 that may perform data storage movement optimizations to automatically relocate or move data between different storage tiers as needed. A determination of on what storage tier to locate data of a data portion may vary with one or more criteria including, for example, the changing I/O workload directed to the data portion over time.

Referring to FIG. 5A, shown is a schematic diagram of the storage array 124 as including a plurality of data devices 61-67 communicating with directors 131-133. The data devices 61-67 may be implemented as logical devices like standard logical devices (e.g., such as thick devices where all storage is allocated or provisioned for the logical device when created) provided in a VMAX® data storage system produced by EMC Corporation of Hopkinton, Mass., for example. In some embodiments, the data devices 61-67 may not be directly useable (visible) to hosts coupled to the storage array 124. Each of the data devices 61-67 may correspond to a portion (including a whole portion) of one or more of the disk drives 42-44 (or more generally physical devices). Thus, for example, the data device section 61 may correspond to the disk drive 42, may correspond to a portion of the disk drive 42, or may correspond to a portion of the disk drive 42 and a portion of the disk drive 43. The data devices 61-67 may be designated as corresponding to different classes, so that different ones of the data devices 61-67 correspond to different physical storage having different relative access speeds or RAID protection type (or some other relevant distinguishing characteristic or combination of characteristics), as further discussed elsewhere herein. Alternatively, in other embodiments that may be used in connection with the system described herein, instead of being separate devices, the data devices 61-67 may be sections of one data device.

As shown in FIG. 5B, the storage array 124 may also include a plurality of thin devices 71-74 that may be adapted for use in connection with the system described herein when using thin provisioning. In a system using thin provisioning, the thin devices 71-74 may appear to a host coupled to the storage array 124 as one or more logical volumes (logical devices) containing contiguous blocks of data storage. Each of the thin devices 71-74 may contain pointers to some or all of the data devices 61-67 (or portions thereof). As described in more detail elsewhere herein, a thin device may be virtually provisioned in terms of its allocated physical storage in physical storage for a thin device presented to a host as having a particular capacity is allocated as needed rather than allocate physical storage for the entire thin device capacity upon creation of the thin device. As such, a thin device presented to the host as having a capacity with a corresponding LBA (logical block address) range may have portions of the LBA range for which storage is not allocated.

Referring to FIG. 5C, shown is a diagram 150 illustrating tables that are used to keep track of device information. A first table 152 corresponds to all of the devices used by a data storage system or by an element of a data storage system, such as an HA 21 and/or a DA 23. The table 152 includes a plurality of logical device (logical volume) entries 156-158 that correspond to all the logical devices used by the data storage system (or portion of the data storage system). The entries in the table 152 may include information for thin devices, for data devices (such as logical devices or volumes), for standard logical devices, for virtual devices, for BCV devices, and/or any or all other types of logical devices used in connection with the system described herein.

Each of the entries 156-158 of the table 152 correspond to another table that may contain information for one or more logical volumes, such as thin device logical volumes. For example, the entry 157 may correspond to a thin device table 162. The thin device table 162 may include a header 164 that contains overhead information, such as information identifying the corresponding thin device, information concerning the last used data device and/or other information including counter information, such as a counter that keeps track of used group entries (described below). The header information, or portions thereof, may be available globally to the data storage system.

The thin device table 162 may include one or more group elements 166-168, that contain information corresponding to a group of tracks on the data device. A group of tracks may include one or more tracks, the number of which may be configured as appropriate. In an embodiment herein, each group has sixteen tracks, although this number may be configurable.

One of the group elements 166-168 (for example, the group element 166) of the thin device table 162 may identify a particular one of the data devices 61-67 having a track table 172 that contains further information, such as a header 174 having overhead information and a plurality of entries 176-178 corresponding to each of the tracks of the particular one of the data devices 61-67. The information in each of the entries 176-178 may include a pointer (either direct or indirect) to the physical address on one of the physical disk drives of the data storage system that maps to the logical address(es) of the particular one of the data devices 61-67. Thus, the track table 162 may be used in connection with mapping logical addresses of the logical devices corresponding to the tables 152, 162, 172 to physical addresses on the disk drives or other physical devices of the data storage system.

The tables 152, 162, 172 may be stored in the global memory 25 b of the data storage system. In addition, the tables corresponding to particular logical devices accessed by a particular host may be stored (cached) in local memory of the corresponding one of the HA's. In addition, an RA and/or the DA's may also use and locally store (cache) portions of the tables 152, 162, 172.

Referring to FIG. 5D, shown is a schematic diagram illustrating a group element 166 of the thin device table 162 in connection with an embodiment of the system described herein. The group element 166 may includes a plurality of entries 166 a-166 f The entry 166 a may provide group information, such as a group type that indicates whether there has been physical address space allocated for the group. The entry 166 b may include information identifying one (or more) of the data devices 61-67 that correspond to the group (i.e., the one of the data devices 61-67 that contains pointers for physical data for the group). The entry 166 c may include other identifying information for the one of the data devices 61-67, including a speed indicator that identifies, for example, if the data device is associated with a relatively fast access physical storage (disk drive) or a relatively slow access physical storage (disk drive). Other types of designations of data devices are possible (e.g., relatively expensive or inexpensive). The entry 166 d may be a pointer to a head of the first allocated track for the one of the data devices 61-67 indicated by the data device ID entry 166 b. Alternatively, the entry 166 d may point to header information of the data device track table 172 immediately prior to the first allocated track. The entry 166 e may identify a cylinder of a first allocated track for the one the data devices 61-67 indicated by the data device ID entry 166 b. The entry 166 f may contain other information corresponding to the group element 166 and/or the corresponding thin device. In other embodiments, entries of the group table 166 may identify a range of cylinders of the thin device and a corresponding mapping to map cylinder/track identifiers for the thin device to tracks/cylinders of a corresponding data device. In an embodiment, the size of table element 166 may be eight bytes.

Accordingly, a thin device presents a logical storage space to one or more applications running on a host where different portions of the logical storage space may or may not have corresponding physical storage space associated therewith. However, the thin device is not mapped directly to physical storage space. Instead, portions of the thin storage device for which physical storage space exists are mapped to data devices, which are logical devices that map logical storage space of the data device to physical storage space on the disk drives or other physical storage devices. Thus, an access of the logical storage space of the thin device results in either a null pointer (or equivalent) indicating that no corresponding physical storage space has yet been allocated, or results in a reference to a data device which in turn references the underlying physical storage space.

FIG. 6 is a flowchart 200 illustrating processing for handling a read of one or more logical tracks of one of the thin devices 71-74 in an embodiment of the system described herein. In a step 202, an appropriate one of the host adapters 32-34 reads the group table 112 of the one of the thin devices 71-74 corresponding to the logical tracks being read. After the step 202, at a test step 204, it is determined whether the logical tracks identified from the group table 112 corresponds to any of the data devices 61-67 (i.e., if there is physical data corresponding to the logical tracks being read). If there is no corresponding physical data (meaning that no logical track(s) were ever written), then processing proceeds to a step 206 where error processing is performed, such as returning a NULL value to the host. Other appropriate error processing may be performed at the step 206. After the step 206, processing is complete.

If it is determined at the step 204 that there is physical data corresponding to the logical tracks being read, then processing proceeds to a step 208 where one or more of the data devices 61-67 associated with the logical tracks being read are identified from the group table 112. After the step 208, processing proceeds to a step 210 where the track table 122 is read from the identified one or more of the data devices 61-67 and the corresponding location of the physical data (i.e., cylinder and track) is determined. As further discussed elsewhere herein, physical storage space may be provided in connection with one data device and/or by a concatenation of multiple data devices or portions thereof. Logical storage space maps to space on the data devices.

After the step 210, processing proceeds to a step 212 where a request may be sent to one or more disk adapters 36-38 corresponding to disk drives 42-44 that provide the physical storage space associated with the identified one of the data devices 61-67 and corresponding location information. After the step 212, processing proceeds to a step 214 where the physical data is read. Note that the data may be stored in a cache or other memory (for example, the memory 46) in connection with being read. In some cases, if the data being read is already in the cache, then the processing at the step 212 and following steps may not be necessary. Note also that reading the data may include updating any metadata used to provide the processing described herein, such as the time last accessed, the host/user making the request, frequency of use, and/or any other appropriate metric. After the step 214, processing proceeds to a step 216 where the data may be received by an appropriate one of the host adapters 32-34 (e.g., by reading the memory 46). After the step 216, processing is complete.

FIG. 7 is a flow chart 300 illustrating processing for handling a write of logical track(s) to one or more of the thin device(s) 71-74 in connection with the system described herein. At a step 302, an appropriate one of the host adapters 32-34 reads the group table 112 of the one of the thin device(s) 71-74 corresponding to the logical tracks being written.

Following the step 302 is a test step 304 where it is determined whether physical space had been previously allocated (i.e., in a prior write operation) for the logical tracks being written. If so, then processing proceeds to a step 306 where the data device that includes the logical tracks is identified. After the step 306, is a step 308 where the track table 122 is read from the identified one or more of the data devices 61-67 and the corresponding location of the physical data (i.e., cylinder and track) is determined. As further discussed elsewhere herein, physical storage space may be provided in connection with one data device and/or by a concatenation of multiple data devices or portions thereof. Logical storage space maps to space on the data devices. Following the step 308 processing proceeds to a step 312 where the data being written is directed to the appropriate physical storage space. The incoming data overwrites the appropriate portion of the data where directed. After the step 312, processing is complete.

If it is determined at the step 304 that there is no physical storage that has been allocated for the logical track(s) being written, then control transfers from the step 304 to a step 314, where a next available data device identifier (i.e., the data device 68) is determined. This information may be obtained from the header 114 of the device table 112. In an embodiment herein, data device identifiers are provided by numbers so that a next available data device identifier is simply one more than a last allocated data device. However, as discussed in more detail elsewhere herein, selection of a data device at the step 314 may include application of other criteria.

After the step 314, processing proceeds to a step 316 where available physical storage space on the disk drives 42-44 is determined. In an embodiment herein, available physical storage space is allocated sequentially from one or more of the disk drives 42-44. Following the step 316 is a step 318 where a request may be sent to a disk adapter 36-38 (or possibly the RA 48 and/or the EA 49) to allocate the physical storage space for the write. Also at the step 318, header info is updated to reflect the newly allocated data device and physical tracks. After the step 318, processing proceeds to the step 312, discussed above, where the data being written is directed to the one or more data devices. After the step 312, processing is complete.

After the read and write processes illustrated in FIGS. 6 and 7, information concerning access of the data, such as access frequency, time of last access or use and/or other characteristics, metrics, and statistics, may be updated and stored by the system described herein. The updated data access information or other characteristic information of the data and/or any portion of the data may, for example, be stored as an entry in a group element of the thin device table 112 (for example, the entry 166 f of the group element 166 as shown in FIG. 5d ). Alternatively, the data characteristic information may be stored in a memory, such as the global memory 46 of the storage device 30, and a pointer to this information stored in the group element 166. Other implementations for storing and access of the data characteristic information are possible.

The allocation of the physical storage space for a thin device at the time of writing the data, as well as the policies that govern the allocation, may be transparent to a user. For example, a user's inquiry into how much storage space is available on a particular thin device may indicate a maximum amount of physical storage space that could be allocated for a thin storage device (provisioned storage space) even though the corresponding physical storage space had not yet been allocated. In an alternative embodiment, the policy for the thin device may be to report something less than the total maximum that could be allocated. In some embodiments, used physical storage space may not exceed 30% of the provisioned storage space.

In an embodiment herein, different portions of the physical data may be automatically moved between different physical disk drives or other storage devices (different tiers) with the same or different characteristics according to one or more policies. For example, data may be initially allocated to a particular fast disk drive, (relatively high tier) but a portion of the data that has not been used over a period of time (for example, three weeks) may be automatically moved, according to the system described herein, to a slower (and perhaps less expensive) disk drive (relatively lower tier). The physical data may then be automatically moved back to the higher tier if the data is subsequently used and/or accessed according to a policy or other criteria (for example, accessed twice in any given week), as further described herein. Thus, the system described herein may operate to automatically move data between tiers according to the one or more policies.

A policy may be configured by an administrator on a system-wide level or may be specific to a particular user on a specific logical device. The system described herein allows for the remapping of physical data based on policy criteria or other metrics and statistics. For example, the policy may be based on the last time data was used and/or accessed. Alternatively, the policy may be based on anticipated use of data over specific times and/or dates. For example, data that is expected to be used at a particular time may be stored on (or relocated to) relatively fast tier and then moved to relatively slow tier when it is expected that the data will not be used again for a lengthy period of time. Moreover, different policies and/or criteria may be implemented corresponding to different users and/or different levels of importance or security of data. For example, it may be known that user A accesses particular data more frequently than user B and, accordingly, the policy for moving physical data according to the system described herein may be to leave more data associated with user A on the relatively fast disk drive as compared with the data associated with user B. Alternatively, user A may access data that is generally of a higher level of importance or requires higher security than that of user B and, accordingly, the system described herein may maintain and/or move more data associated with user A on a disk drive that is relatively more reliable, available and/or secure as compared with the data associated with user B.

In an embodiment herein, data may be moved between physical disk drives (or other physical storage) having different characteristics, such as speed, cost, reliability, availability, security and/or other characteristics. As discussed elsewhere herein, logical data devices may be established having different classes corresponding to characteristics of the physical disk drives (or other physical storage) to which the data devices are mapped. Further, it should be noted that any section of the logical device may be moved according to the system described herein based on the characteristics of the data (and governed by default or specific policies).

FIG. 8 is a flowchart 400 illustrating processing for copying and remapping physical data according to the system described herein. In a step 402, space for a group of tracks is allocated on a second data device having a different class (e.g, different storage tier) from that of a first data device (data source). The first data device has a first storage class that is different from a second storage class of the second data device. For example, the second data device may be mapped to a physical disk drive that is slower than that of the first data device of the first class, as further discussed elsewhere herein. After the step 402, processing proceeds to a step 404 where data associated with the data device of the first class is copied to a location corresponding to the data device of the second class. After the step 404, processing proceeds to a step 406 where the group table of the thin device is updated in accordance with the remapping. After the step 406, processing proceeds to a step 408 where the group of tracks associated with the data device of the first class, from which the data was copied, is deallocated, freeing the locations for future use.

FIG. 9 is a flowchart 500 illustrating implementation of a policy for data storage and management in connection with an embodiment of the system described herein. In a step 502, certain characteristics of stored data are identified (for example, from the group element 166, as discussed elsewhere herein). In various embodiments, the characteristics may include usage information such as when the stored data was last accessed and/or how often the stored data has been accessed over a specific time period (for example, hours, days, weeks, etc.). It is also possible to determine how long (on average or in aggregate) it has taken to service each specific I/O request to the data. As further discussed elsewhere herein, the characteristics may also include particular user information corresponding to the stored data.

After the step 502, processing proceeds to a step 504 where policy information is accessed. The policy information provides the specific criteria used for data storage and management. After the step 504, processing proceeds to a step 506 where the policy is applied to the stored data. The policy may include criteria used for managing stored data such as criteria concerning frequency of use of data and/or criteria with respect to specific users and/or other criteria, such as file name, file type, file path, requesting application, expected time to re-use of the data, temporary storage only, life expectancy of the data, data type (e.g., compressed, encrypted, de-duped) and/or protection requirements of the data (e.g., store on an encrypted tier). The policy may be applied to identify data for lifecycle management according to characteristics of entire data volumes or any portions thereof. The policy may also consider the access history, effective performance or other characteristics about the data that might be utilized to optimize the performance, cost, availability or retention requirements of the data.

After the step 506, processing proceeds to a step 508 where the data for which characteristics have been determined is managed according to the policy and based on the characteristics of the data. For example, data that is frequently used may be moved to a relatively fast storage device whereas data that has not been used over a certain period of time may be moved to a relatively slow storage device according to the data processing as discussed elsewhere herein. As noted herein, the data that is moved may be entire data volumes or portions thereof. As discussed elsewhere herein, it may be possible to provide fairly sophisticated analysis to determine whether to promote data (move to a relatively faster storage device) or demote data (move to a relatively slower storage device).

After the step 508, processing proceeds to a test step 510 where it is determined if another policy with other criteria should be applied to the stored data being managed. If an additional policy is to be applied, then processing proceeds to the step 506. If no further policies are to be applied, then processing proceeds to a test step 512 where it is determined whether there is more data to be managed according to the system described herein. If there is further stored data to manage, then processing proceeds back to the step 502. If no further stored data is to be managed, then after the test step 512, processing is complete. In some cases, tracking, avoiding and resolving conflicting priorities would be handled to ensure that two policies do not create a “ping-pong” effect, moving data blocks up- and down-in a never ending cycle.

As discussed elsewhere herein, the data devices 61-67 may be associated with physical storage areas (e.g., disk drives, tape, solid state storage, etc.) having different characteristics. In various embodiments, the physical storage areas may include multiple tiers of storage in which each tier of storage areas and/or disk drives that may be ordered according to different characteristics and/or classes, such as speed, technology and/or cost. The thin devices 71-74 may appear to a host coupled to the storage device 30 as a logical volume (logical device) containing a contiguous block of data storage, as discussed herein. Each thin device 71-74 may correspond to a particular data device, a portion thereof and/or multiple data devices. Accordingly, each thin device 71-74 may map to storage areas across multiple storage tiers. As a result, although each thin device 71-74 may appear as containing a logically contiguous block of storage, each thin device 71-74 may allow for blocks of data to be transparently stored (and/or retrieved) from discontiguous storage pools made up of the varying classes of data storage devices. In this way, the granularity at which the system for tiered storage described herein operates may be smaller than at the file level, for example potentially as small as a single byte, but more practically at the granularity of a single logical block or collection of sequential data blocks. A data block may be of any size including file system or database logical block size, physical block, track or cylinder and/or other size. Multiple data blocks may be substantially the same size or different sizes, such as different size data blocks for different storage tiers or different sized data blocks within a single storage tier.

FIG. 10 is a schematic illustration of a fine grained tiered storage system 600 according to an embodiment of the system described herein. A storage system 630 is shown including a thin device 620, like the thin devices 71-74 discussed elsewhere herein, that may be coupled to multiple physical storage devices across multiple storage tiers. As discussed elsewhere herein, the storage tiers may be associated with data devices, like the data devices 61-67 discussed herein, so that, for example, there is one data device for each storage tier, one data device for multiple storage tiers, any portion of a data device for any portion of the pools of storage shown for the storage tiers, and/or any combinations thereof. For example, in an embodiment, a top tier storage pool 610 (e.g., tier 0) may include flash/solid state disk (SSD) drives that are relatively fast and expensive. Other storage pools 611-613 (e.g., tiers 1-3) may include disk drives of decreasing speeds or other configurations (i.e., 15 k rpm, 10 k rpm, 7.5 k rpm redundant array of independent disk (RAID) storage). The lowest tier of storage pool 614 (e.g., tier 4) may include, for example, tape storage, largest capacity disk drives (such as massive array of idle disks (MAID) storage). As illustrated, the last storage tier 614 may include storage devices from other storage systems that are external to the storage system 630 where such external storage devices may be suitable for long term storage of data that is infrequently accessed. However, note that external storage could have specific characteristics such as tape, or might perform additional processing to optimize the storage of data, such as de-duplication. In some embodiments, external storage might be used to support tier 2 or tier 3 class applications.

The thin device 620 may map to different storage areas (devices) across multiple tiers. As discussed elsewhere herein, the granularity of the system may be less than at the file level and allow for blocks of data of any size to be stored across multiple storage tiers 610-613 of the storage system 630 in a process that is transparent to the host and/or host application. For example, in the illustrated embodiment, the thin device 620 may map blocks of data to storage areas (devices) such as a storage area 610 a in the pool of storage of the top storage tier 610, a storage area 611 a in the pool of storage of the next storage tier 611, storage areas 612 a, 612 b in pool of storage of the next storage tier 612, and storage areas 613 a, 613 b, 613 c in the pool of storage of the next storage tier 613. As discussed elsewhere herein, the last storage tier 614 may include external storage and the system described herein may map to a storage area 614 a in the pool of storage in the tier 614.

Mirroring (backup) of data may also be facilitated by tiered storage across multiple tiers according to the system described herein. For example, data that is accessed frequently may be stored on a fast storage device (tier 0) while a mirrored copy of the data that is not expected to be accessed may be stored on a slower storage device in one or more other tiers (e.g., tiers 1-4). Accordingly, the same data may be stored on storage devices of multiple tiers of storage pools.

FIG. 11 is a schematic illustration showing a fine grained tiered storage system 700 according to an embodiment of the system described herein. As illustrated, a storage device 730 includes multiple thin devices 720-722 and multiple pools of storage in multiple storage tiers 710-713. Host applications 740-744 and/or other entities (e.g., other storage devices, SAN switches, etc.) request data writes and data reads to and from the storage device 730. In various embodiments, multiple host applications 740-744 may share a single one of thin devices 720-722 and/or multiple thin devices 720-722 may be mapped to the same set of storage pools 710-713.

In an embodiment herein, a write target policy may be applied to data that is being written according to the system described herein. For example, data that is expected to be used frequently, for example database indices, may be initially written directly to fast storage (e.g., tier 0 flash/SSD storage) whereas data that is not expected to be accessed frequently, for example backup or archived data, may be initially written to slower storage devices (e.g., tier 4 MAID or external storage). In this manner, data is efficiently stored by targeting the write to storage areas and devices according to the estimated or expected access frequency of the data, beginning with the initial write of the data and also applying to subsequent data writes that jump across multiple tiers.

The process for determining the appropriate target storage location of the write of the data may be made based on the logical unit number (LUN) ID of the device from which the data is being written, where the storage device 730 may have or obtain information about the types of data stored on specific logical units. Alternatively, additional policies and capabilities may be enabled by adding host-resident “extension” software, for example to tag I/O requests with information about the requesting application or user so that the determination may be made based on other information provided by the host and/or entity accessing the storage device 730 (e.g., a target policy indicator provided with each write or class of writes). Other possible criteria include the time of day, the size of the incoming write operation (e.g. very large sequential writes vs. smaller random writes), file name, file type, host OS type, data type, access patterns, inter-dependent accesses to other data, etc. It is also possible that “hints” from the host could also be used, particularly relating to performance and availability requirements of the data, etc.

The system described herein may include automatic promotion and demotion policies to facilitate optimization of performance, storage availability and power. For example, a least recently used (LRU) policy may be used to demote data blocks in order to pro-actively make room for new writes of data blocks and/or promotions of data blocks within the system. A most frequently used (MRU) policy may be used to promote data blocks that are frequently used to faster storage tiers. Predictive policies may be used to recognize that data blocks that will be needed before they are actually needed and promote the data blocks accordingly (for example, nightly batch jobs, etc.). Alternatively, the system described herein may include an application programming interface (API) that allows a hosts/users/applications to inform the storage that certain blocks should be promoted or demoted to different tiers. Note that promotion and demotion may relate to a relative ordering of tiers where promotion refers to moving data to physical storage that is relatively faster and demotion refers to moving data to physical storage that is relatively slower.

Other special purpose policies may also be used. As discussed elsewhere herein, mirroring of data blocks across multiple tiers may be used. For example, for frequently used data blocks, one copy may be written to flash/SSD memory at a top storage tier and a second copy mirrored to another storage tier (e.g., tier 3 or tier 4). Another policy may include promoting and/or demoting a data block, but not deleting the data block from its pre-promoted or demoted location until the data block is modified. This policy offers advantages including when subsequently demoting the block (if unmodified), a copy may already exist on a slower storage tier and an additional copy does not need to be made (only the copy on the faster storage tier deleted). When a data block is modified, the previous copy on a different storage tier may be deleted.

Other policies may include manual or automatic pre-promotion and post-demotion policies. For example, blocks may be promoted in the background immediately before batch runs (e.g., billing runs etc.). Additionally, writes for such processes as back-ups may require the fastest possible write, but never (or only infrequently) read. In this case, writes may be written to a top storage tier and immediately scheduled for demotion to a lower storage tier. With MAID storage, data blocks that are rarely or never used may be consolidated onto individual spindles that may then be powered off, providing a reduction in power consumption for storage of data blocks infrequently accessed. Further, sequential/contiguous blocks may be coalesced and relocated in an optimization process that may include other advanced strategies, including aligning indices near to data being indexed. It is also possible to have a de-duplication policy in which nothing is deleted from storage in a de-dup tier. Data blocks in storage pools of a de-dup storage tier may be promoted to fast storage tiers as needed, but block and index/metadata in the de-dup storage may be maintained even if a data block is promoted to a faster storage tier and modified or deleted. Maintenance of de-dup storage tiers may involve “use counters” and/other mechanisms that may be used with known data cleaning processes such as garbage collection, etc.

In an embodiment herein, one or more policies may be provided to guarantee a particular level of performance and/or that a particular percentage of data is to be provided on storage having certain characteristics (e.g., speed). The policy may guarantee a minimum number for I/Os per second (IOPS) and/or may guarantee greater than a minimum IOPS for any I/O operation.

FIG. 12 is a flowchart 800 of processes for writing data blocks in a fine grained tiered storage system based on one or more policies according to an embodiment of the system described herein. At a step 802, a request for a write of data is received by a thin device or other logical device associated with a storage device, as described herein. After the step 802, processing proceeds to a step 804 where information associated with the data block is determined. For example, as further discussed elsewhere herein, the information may be the logical unit number (LUN) ID of the device from which the data is being written and/or may other information provided by the host and/or other entity accessing the storage device. After the step 804, processing proceeds to a step 806 where a write target policy is accessed. For example, as further discussed elsewhere herein, the write target policy may specify that data that is expected to be used frequently may be initially written directly to faster storage in a first storage tier whereas data that is not expected to be accessed frequently may be initially written to slower storage devices in a lower storage tier.

After the step 806, processing proceeds to a step 808 where the determined information associated with the data is processed according to the target policy and the data block is written to a storage location in the storage device according thereto. Accordingly, the data block may initially be written to a storage area (device) in a pool of storage of a storage tier corresponding to the anticipated frequency of use of the data block and/or according to other criteria. After the step 808, processing proceeds to a step 810 where information concerning the location of the data block is updated in a table of information in the thin device, as further discussed elsewhere herein. After the step 810, processing is complete.

In some cases, there may be insufficient available free space to write data to the storage tier corresponding to the storage policy at the step 808. This may be addressed in a number of ways. One possibility is to maintain the data in cache memory until space becomes available, which can occur when data is moved from the target tier as a result deletion of promotion/demotion based on storage policies. Note also that it is possible to temporarily store the data in a lower tier, and then schedule the data for promotion to the appropriate tier using any appropriate mechanism, such as setting a flag that causes the data to be promoted before any other data.

FIG. 13 is a flowchart 820 illustrating steps performed in connection with writing data to a storage tier that may be full. Processing begins in the first test step 822 where it is determined if the storage tier is full. If not, then control passes from the test step 822 to a step 824 where the data is written to the storage tier. Following the step 824, processing is complete.

If it is determined at the test step 822 that the storage tier is full, then control passes from the test step 822 to a step 826 where wait processing is performed. The wait at the step 826 could be for any appropriate amount of time. Following the step 826, control passes back to the test step 822 for a new iteration.

FIG. 14 is a flowchart 830 that illustrates an alternative embodiment for handling write operations to a storage tier that may be full. Processing begins at a first test step 832 where it is determined if the storage tier is full. If not, then control passes from the test step 832 to a step 834 where the data is written to the storage tier. Following the step 834, processing is complete.

If it is determined at the test step 832 that the storage tier is full, then control passes from the test step 832 to a step 836 where the data is written to a different storage area, such as a lower (or higher) storage tier or to global memory of the storage device (e.g., cache memory), as further discussed herein. The data may be placed in the different storage area temporarily. Following the step 836 is a step 838 where the data is scheduled to be moved to the appropriate storage area (the originally-destined storage tier). Following the step 838, processing is complete.

In an embodiment, at the step 836, the write data may be temporarily stored in a global memory, such as the global memory 46, until storage space in the particular requested tier becomes available that is sufficient to handle the write request. At the step 838, scheduling for the movement of the data may include relocating data in the particular requested tier, e.g. “faster” storage tier, to a lower tier, e.g. “slower” storage tier, to make memory available for the data temporarily stored in the global memory. In another embodiment, at the step 836, data for the requested write may be immediately written to a lower tier than that requested for the write and, at the step 838, a future promotion of the data to the particular requested higher tier (originally-destined storage tier) may be scheduled. The embodiments discussed herein provide for the dynamic re-allocation and re-ordering of data to accommodate write policies, usage patterns and the like.

FIG. 15 is a flowchart 900 of processes for promoting and demoting data blocks in a fine grained tiered storage system according to an embodiment of the system described herein. At a step 902, characteristics of a data block are assessed or otherwise determined. As further discussed elsewhere herein, characteristics may include access frequency of the data block, time of last access or use, information associated with particular users of the data block and/or other characteristics and statistics information. The characteristics may be assessed periodically, at a determined time, after the occurrence of a trigger event and/or based on some other criteria. After the step 902, processing proceeds to a step 904 where a policy is accessed related to promotion and/or demotion of data blocks between multiple storage tiers. Policies may be accessed automatically or manually as discussed elsewhere herein and include such policies as LRU, MFU, predictive policies and/or special purpose policies. After the step 904, processing proceeds to a test step 906 where it is determined if a different policy is to be selected. In some instances, it may be useful to be able to dynamically select the policy to be used based on characteristics of the data and/or some other criteria, such as dynamic run time conditions. For example, a first policy may be used for tier 4 data that was recently moved from tier 3 while a second policy may be used for tier 4 data that has been tier 4 data for a relatively long period of time. If a different policy is to be selected, processing proceeds back to the step 904. Otherwise, processing proceeds to a step 908.

At the step 908, data blocks are to be promoted and/or demoted according to the one or more policies. If a data block is promoted, the data block is moved to a storage area (device) in a pool of storage of a higher storage tier, for example faster storage. If a data block is to be demoted, the data block is moved to a storage area (device) in a pool of storage of a lower storage tier, for example slower storage. As further discussed elsewhere herein, in some cases, the promotion and/or demotion procedure may include moving copies of data blocks to other storage tiers and the deleting the old data blocks from their original storage location and/or copies of data blocks previously stored at the subsequent storage tiers may be used and “movement” of the data block is to make the previously-stored version of the data block become again the current, accessible data block.

After the step 908, processing proceeds to a step 910 where information concerning the location of the data block is updated in a table of information in the thin device, as further discussed elsewhere herein. After the step 910, processing proceeds to a test step 912 where it is determined whether additional stored data is to be managed according to the system described herein. If more stored data is to be managed (promoted/demoted), processing proceeds back to the step 902. Otherwise, processing is complete. Note that data access may be guaranteed even while data is being moved from one tier to another.

In principal, the advantages of a multi-tiered configuration increase as the size of the storage portions for which optimal tier selection are performed decreases. However, the use of smaller portions may result in the need to determine optimal placement for a significant number (e.g., billions) of regions. Thus, there are challenges presented in connection with scaling a tiering system for a relatively large storage area. In the system described herein, the overall process of optimizing tier usage is divided into a movement policy determination operation and an operation that applies the movement policy (moves the storage regions to the optimal tier for that region per the movement policy), in such a way that the movement policy determination operation can, if desired, be executed on processing hardware separate from that used by the movement policy application operation. For example, in some embodiments, the movement policy application operation may execute on a storage array containing the data and the movement policy determination operation may execute on a processing complex that is separate from the storage array, so that the movement policy determination operation can take advantage of larger processing and/or memory capacity than is available on the storage array. The system described herein provides that the movement policy may specify the preferred tier for a region of storage as a (statically defined) function of the host access rate (or other metrics) for the storage region. This allows a given instance of the movement policy to have longer useful life than a movement policy that specifies the preferred tier of a region of storage simply as a function of the logical address of the region since, with the system described herein, the preferred tier for a given region can change as a result of a change in the host access rate (or other metrics) for the region, even without a change to the movement policy. Furthermore, such a movement policy enables embodiments in which the movement policy determination operation can be performed without needing an input indicating which tier a given storage region is currently mapped to. Note that the movement policy determination and movement policy application operations may in turn be implemented in a distributed fashion in a given embodiment and, as will be discussed herein, may be optimized to minimize execution time and to minimize the adverse impacts of storage movement on storage system performance.

As discussed elsewhere herein, policies may be used to determine when to promote data (map the data to a relatively faster tier) and when to demote data (map the data to a relatively slower tier). In an embodiment herein, each of the storage portions may correspond to an extent, where each extent corresponds to forty-eight sub-extents, and each sub-extent corresponds to ten chunks and each chunk corresponds to twelve tracks, so that an extent includes four hundred and eighty chunks (five thousand seven hundred and sixty tracks). Note also that, for the same logical device, different ones of the extents may have different sizes. Note also that the storage space may be one or more of a single logical device, a group of logical devices, all logical devices corresponding to particular physical space, logical devices corresponding to a particular application or set of application, etc.

Thin devices and thin provisioning are described in more detail in U.S. patent application Ser. No. 11/726,831, filed Mar. 23, 2007 (U.S. Patent App. Pub. No. 2009/0070541 A1), AUTOMATED INFORMATION LIFE-CYCLE MANAGEMENT WITH THIN PROVISIONING, Yochai, EMS-147US, and U.S. Pat. No. 7,949,637, Issued May 24, 2011, Storage Management for Fine Grained Tiered Storage with Thin Provisioning, to Burke, both of which are incorporated by reference herein.

As discussed elsewhere herein, the data devices 61-67 (and other logical devices) may be associated with physical storage areas (e.g., disk drives, tapes, solid state storage, etc.) having different characteristics. In various embodiments, the physical storage areas may include multiple tiers of storage in which each sub-tier of physical storage areas and/or disk drives may be ordered according to different characteristics and/or classes, such as speed, technology and/or cost. The data devices 61-67 may or may not appear to a host coupled to the storage array 124 as a logical volumes (logical devices) containing a contiguous block of data storage, as discussed herein. Accordingly, each of the data devices 61-67 may map to storage areas across multiple physical storage drives. The granularity at which the storage system described herein operates may be smaller than at the file level, for example potentially as small as a single byte, but more practically at the granularity of a single logical block or collection of sequential data blocks. A data block may be of any size including file system or database logical block size, physical block, track or cylinder and/or other size. Multiple data blocks may be substantially the same size or different sizes, such as different size data blocks for different storage volumes or different sized data blocks within a single storage volume.

In accordance with techniques herein, an embodiment may allow for locating all of the data of a single logical portion or entity in a same tier or in multiple different tiers depending on the logical data portion or entity. In an embodiment including thin devices, the techniques herein may be used where different portions of data of a single thin device may be located in different storage tiers. For example, a thin device may include two data portions and a first of these two data portions may be identified as a “hot spot” of high I/O activity (e.g., having a large number of I/O accesses such as reads and/or writes per unit of time) relative to the second of these two portions. As such, an embodiment in accordance with techniques herein may have added flexibility in that the first portion of data of the thin device may be located in a different higher performance storage tier than the second portion. For example, the first portion may be located in a tier comprising flash devices and the second portion may be located in a different tier of FC or SATA drives.

Data used in connection with techniques herein, such as the performance data of FIG. 3 used in determining response time and/or other performance metrics for physical device(s), may be obtained through observation and monitoring actual performance with respect to read and write requests or commands from the DA, controller or other backend physical device interface.

It should be noted that movement of data between tiers from a source tier to a target tier may include determining free or unused storage device locations within the target tier. In the event there is an insufficient amount of free of unused storage in the target tier, processing may also include displacing or relocating other data currently stored on a physical device of the target tier. An embodiment may perform movement of data to and/or from physical storage devices using any suitable technique. Also, any suitable technique may be used to determine a target storage device in the target tier where the data currently stored on the target is relocated or migrated to another physical device in the same or a different tier.

One embodiment in accordance with techniques herein may include multiple storage tiers including a first tier of flash devices and one or more other tiers of non-flash devices having lower performance characteristics than flash devices. The one or more other tiers may include, for example, one or more types of disk devices. The tiers may also include other types of SSDs besides flash devices.

As described above, a thin device (also referred to as a virtually provisioned device) is a device that represents a certain capacity having an associated address range. Storage may be allocated for thin devices in chunks or data portions of a particular size as needed rather than allocate all storage necessary for the thin device's entire capacity. Therefore, it may be the case that at any point in time, only a small number of portions or chunks of the thin device actually are allocated and consume physical storage on the back end (on physical disks, flash or other physical storage devices). A thin device may be constructed of chunks having a size that may vary with embodiment. For example, in one embodiment, a chunk may correspond to a group of 12 tracks (e.g., 12 tracks*64 Kbytes/track=768 Kbytes/chunk). As also noted with a thin device, the different chunks may reside on different data devices in one or more storage tiers. In one embodiment, as will be described below, a storage tier may consist of one or more storage pools. Each storage pool may include multiple logical devices which are data devices and their associated physical devices. With thin devices, a system in accordance with techniques herein has flexibility to relocate individual chunks as desired to different devices in the same as well as different pools or storage tiers. For example, a system may relocate a chunk from a flash storage pool to a SATA 7.2K RPM storage pool. In one embodiment using techniques herein, a thin device can be bound to a particular storage pool of a storage tier at a point in time so that any chunks requiring allocation of additional storage, such as may occur when writing data to the thin device, result in allocating storage from this storage pool. Such binding may change over time for a thin device.

Referring to FIG. 16A, shown is an example 700 illustrating use of a thin device in an embodiment in accordance with techniques herein. The example 700 includes three storage pools 712, 714 and 716 with each such pool representing a storage pool of a different storage tier. For example, pool 712 may represent a storage pool of tier A of flash storage devices, pool 714 may represent a storage pool of tier B of FC 15K RPM rotating disk drive storage devices, and pool 716 may represent a storage pool of tier C of SATA 7.2K RPM rotating disk drive storage devices. Each storage pool may include a plurality of logical devices (which are data devices) and associated physical devices (or portions thereof) to which the logical devices are mapped. Element 702 represents the thin device address space or range including chunks which are mapped to different storage pools. For example, element 702 a denotes a chunk C1 which is mapped to storage pool 712 and element 702 b denotes a chunk C2 which is mapped to storage pool 714. Element 702 may be a representation for a first thin device which is included in a storage group of one or more thin devices.

It should be noted that although the example 700 illustrates only a single storage pool per storage tier, an embodiment may also have multiple storage pools per tier.

Referring to FIG. 16B, shown is an example representation of information that may be included in an allocation map in an embodiment in accordance with techniques herein. An allocation map may be used to identify the mapping for each thin device (TD) chunk (e.g. where each chunk is physically located). Element 760 represents an allocation map that may be maintained for each TD. In this example, element 760 represents information as may be maintained for a single TD although another allocation map may be similarly used and maintained for each other TD in a storage group. Element 760 may represent mapping information as illustrated in FIG. 16A such as in connection the mapping of 702 to different storage pool devices. The allocation map 760 may contain an entry for each chunk and identify which logical device or data device and associated physical storage is mapped to the chunk. For each entry or row of the map 760 corresponding to a chunk, a first column 760 a, Chunk ID, denotes an identifier to uniquely identify the chunk of the TD, a second column 760 b, indicates information about the data device and offset to which the chunk is mapped, and a third column storage pool 760 c denotes the storage pool and tier including the data device of 760 b. For example, entry 762 represents chunk C1 illustrated in FIG. 16A as 702 a and entry 764 represents chunk C2 illustrated in FIG. 16A as 702 b. It should be noted that although not illustrated, the allocation map may include or otherwise use other tables and structures which identify a further mapping for each data device such as which physical device locations map to which data devices. This further mapping for each data device, as well as other logical devices generally, is described and illustrated elsewhere herein such as, for example, with reference back to FIG. 5B. Such information as illustrated and described in connection with FIG. 16B may be maintained for each thin device in an embodiment in accordance with techniques herein.

In connection with performing I/O operations, such as writes as well as reads, a data storage system in an embodiment in accordance with techniques herein may use a cache in order to improve performance.

In connection with collecting statistics or metrics characterizing performance, workload and/or activity for a thin device, one approach may be to collect the information per chunk or, more generally, for the smallest level of granularity associated with allocation and de-allocation of storage for a thin device. Such statistics may include, for example, a number of reads/unit of time, #writes/unit of time, a number of pre-fetches/unit of time, and the like. However, collecting such information at the smallest granularity level may not scale upward as number of chunks grows large such as for a single thin device which can have up to, for example 300,000 chunks.

Therefore, an embodiment in accordance with techniques herein may collect statistics on a grouping of “N” chunks also referred to as an extent, where N represents an integer number of chunks, N>0. N may be, for example, 480 in one embodiment. Each extent may represent a consecutive range or portion of the thin device in terms of thin device locations (e.g., portion of the address space or range of the thin device). Note that the foregoing use of consecutive does not refer to physical storage locations on physical drives but rather refers to consecutive addresses with respect to a range of addresses of the thin device which are then mapped to physical device locations which may or may not be consecutive, may be on the same or different physical drives, and the like. For example, in one embodiment, an extent may be 480 chunks (N=480) having a size of 360 MBs (megabytes).

An extent may be further divided into sub extents, where each sub extent is a collection of M chunks. M may be, for example 10 in one embodiment. In one embodiment, the sub-extent size may correspond to the smallest granularity of data movement. In other words, the sub extent size represents the atomic unit or minimum amount of data that can be operated upon when performing a data movement such as between storage tiers.

Referring to FIG. 16C, shown is an example illustrating partitioning of a thin device's address space or range in an embodiment in accordance with techniques herein. The example 250 includes a thin device address space or range 252 which, as described elsewhere herein, includes chunks mapped to physical storage locations. The thin device address space or range 252 may be partitioned into one or more extents 254 a-254 n. Each of the extents 254 a-254 n may be further partitioned into sub-extents. Element 260 illustrates that extent X 254 n may include sub extents 256 a-256 n. Although only detail is illustrated for extent 254 n, each of the other extents of the thin device also includes a same number of sub extents as illustrated for 254 n. Each of the sub extents 256 a-256 n may represent a grouping of “M” chunks. Element 262 illustrates that sub extent 1 256 a may include chunks 258 a-258 n. Although only detail is illustrated for sub extent 256 a, each of the other sub extents 256 b-256 n also includes a same number of “M” chunks as illustrated for 256 a. Thus, each of the extents 254 a-254 n may represent an grouping of “N” chunks, where

N=# sub extents/extent*M chunks/sub extent

An embodiment in accordance with techniques herein may collect statistics for each extent or other suitable level of granularity.

In one embodiment in accordance with techniques herein, a chunk may represent the size of a single atomic allocation unit or amount of storage allocated in connection with a thin or virtually provisioned device. Statistics may be collected for each extent and the sub-extent may represent the smallest level of granularity (e.g, unit of storage) for which data movements may be performed such as between storage tiers. For thin or virtually provisioned logical devices (e.g. LUNs, storage may be allocated at a chunk level (e.g., a single chunk may denote the allocation unit).

In an embodiment in accordance with techniques herein, an SLO (service level objective) may be specified for one or more logical devices of a customer or tenant having data stored on the data storage system. In one embodiment in accordance with techniques herein, the data storage system may provide a multi-tenant (MT) environment whereby multiple tenants, or customers, store their data on the data storage system. In such an exemplary MT environment, a different service level objective or SLO may be specified for each tenant that defines a guaranteed performance level or performance goal for the tenant. For example, an SLO may be related to a guaranteed level of performance with respect to I/O operations serviced at the data storage system for the tenant. In this case, the SLO specified for the tenant may be expressed in terms of one or more metrics, such as based on response time (RT). For example, the SLO specified for the tenant may include an average response time (RT) with respect to I/Os issued by the tenant. To further illustrate, an SLO may specify an average RT of 3 milliseconds (ms.) for the tenant whereby the tenant is guaranteed to have an average RT of 3 ms. for each LUN storing the tenant's data. The tenant may also be referred to as a customer or consumer of the data storage system having its data stored on the data storage system. A single tenant or customer may be, for example, one or more applications executing on a host. A single host may have one or more tenants or customers where each of the tenants or customers includes one or more applications. For simplicity of illustration, following examples may refer to a single application on a host as a tenant or customer for which an SLO is specified where the SLO may be applied to each LUN used by the application. However, it will be appreciated by those skilled in the art that an SLO, such as RT, specified for a single tenant or customer may be applied in the aggregate with respect to multiple applications and associated LUNs of the single tenant or customer.

The SLO may include an RT denoting a guaranteed level of performance as measured on the data storage system where the RT denotes an average RT per LUN. For example, the SLO may specify an RT for an application's LUNs. The application may be a database application and the SLO may specify a RT to be guaranteed for each of the LUNs used the application.

The SLO may be associated with a general level of service purchased by the customer. For example, in one embodiment, a data storage customer or tenant may purchase one of five defined performance level plans: diamond, platinum, gold, silver and bronze. The foregoing listing may denote an order from highest to lowest service plan level. In such an embodiment the highest ranked service plan level of diamond may have the most stringent or highest performance objective of all service plans. In contrast, the lowest ranked service plan level of bronze may have the lowest performance objective of all service plans. For example, the diamond service plan may have an SLO that is an average RT=2 ms with respect to all I/Os of all LUNs of the customer, and the bronze service plan may have an SLO that at is an average RT=15 ms with respect to all I/Os of all LUNs of the customer. It should be noted that generally an embodiment may include any number of service levels and plans.

Additionally, although examples and illustrations herein may refer to a RT specified as an SLO, it should be noted that an SLO may be specified using one or more other metrics other than RT. For example, I/O related SLOs may be specified in terms of guaranteed I/O throughput (e.g., I/O rate such as I/Os per second), data throughput (e.g., megabytes per second), and the like. An SLO, such as the RT SLO described herein, may be applied on a per LUN level (e.g., guaranteed for each LUN individually). An embodiment may also specify an I/O related SLO such as RT which may be guaranteed at a different level of granularity than per LUN. For example, the RT SLO may be guaranteed as an aggregate average RT for the tenant or customer and thus as an average RT determined with respect to I/Os issued to all LUNs of the tenant or customer. As another variation where a tenant includes multiple applications, the RT SLO may be guaranteed at the application level (e.g., the RT SLO is guaranteed for each individual application of the tenant across all LUNs used by each individual application).

In one embodiment described following paragraphs, there may be five service levels or plans as noted above each specifying a per logical device RTO performance goal that is a maximum average RT measured for a logical device. The SLO may be met or maintained if the observed average RT over some time period is less than (or equal to or less than) the RTO of the SLO for each individual logical device (e.g., LUN that is a thin device, thick device or regular LUN, etc.) of the customer. The observed average RT may be determined with respect to front end or host I/O operations directed to the logical device.

As mentioned elsewhere herein, each host or front end I/O may be translated or result in N backend physical device I/Os, where N is one or more. The value of N for each host write operation directed to a LUN, such as a thin device, may vary with the particular RAID level and configuration from which storage is provisioned for the LUN. In particular, if the LUN is a thin or virtually provisioned LUN, the value of N for each host write I/O directed to a data portion (e.g., chunk) of a LUN may vary with the particular RAID level and configuration from which storage is provisioned for the individual data portion of the LUN. As described herein, for a thin device, storage may be allocated for a data portion the first time data is written to the logical address associated with the data portion. For a host write operation to store data in physical storage location of a RAID group, the foregoing value of N will be more than one and may be generally referred to as a write amplification of the single host write or the amplification of I/O workload depending on the RAID protection type and configuration. The value of N for a single host write operation may denote an expected write penalty or cost associated with writing data to a physical storage location in a particular RAID group. For example, consider an embodiment in accordance with techniques herein that supports the following RAID protection types and configurations of RAID-1, RAID-5 and RAID-6 known in the art. As known in the art, each RAID type or level (e.g., RAID-n) may specify a different type or level of data storage protection. A RAID group configuration uses multiple physical devices to provide a combination of fault tolerance and/or improved performance for data storage devices. For example, a RAID-1 group is configured to provide mirroring of each data portion written to the RAID group and includes at least 2 PDs. Each host write to a RAID-1 group results in 2 backend or PD writes. A RAID-5 group includes multiple PDs and provides protection from a single PD failure with block level striping and distributed parity information. For example, a RAID-5 group may be configured to include 3 data drives and 1 parity drive meaning that the RAID-5 group includes at least 4 PDs and each host write may result in at least 2 backend or PD reads (e.g., of other user data needed to compute parity information) and 2 backend or PD writes (e.g., 1 parity write and 1 data write for the newly written data). Another possible RAID-5 configuration may be 7 data drives and 1 parity drive where each host write may result in at least 6 backend or PD reads (e.g., of other user data needed to compute parity information) and 2 backend or PD writes (e.g., 1 parity write and 1 data write for the newly written data). RAID-6 provides protection from two PDs of the RAID group failing with two sets of distributed parity and block level striping. For example, a RAID-6 group may be configured to include 4 data drives and 2 parity drives meaning that the RAID-6 group includes at least 6 PDs and each host write may result in at least 3 backend PD reads (e.g., of the other user data needed to compute parity information) and 3 backend PD writes (e.g., 2 parity writes and 1 data write for the newly written data).

The particular RAID levels described herein are merely exemplary and not a limitation of the techniques described herein. Generally, any suitable RAID level and configuration may be used each having an associated write penalty or cost.

An embodiment in accordance with techniques herein may have multiple RAID levels and configurations for each media type or PD technology. For example, an embodiment may support RAID-1, RAID-5 and RAID-6 for each possible PD type of EFD and each possible rotating disk drive type (e.g., FC 10K RPM, FC 15K RPM, SATA 7.2K RPM, SAS 10K RPM, NL-SAS 15K RPM, and the like). Although all such combinations may be supported, an embodiment of a data storage system in accordance with techniques herein may actually include configured RAID groups for a portion of those supported combinations. For example, an embodiment may include configured RAID-1 and RAID-5 groups for each of SATA 8.2K RPM and FC 15K RPM drives and may include configured RAID-5 and RAID-6 groups for EFD drives. It may be that performance is unacceptable for certain configurations, such as a RAID-6 group of 7.2 K RPM SATA drives.

In one embodiment in accordance with techniques herein as described in more detail below, the SLO associated with a thin or virtually provisioned logical device may be used to select the physical storage location for the first or initial storage allocation. As described herein, a chunk of physical storage for a thin device portion, such as a chunk, may be allocated upon the first or initial write to a logical address associated with that chunk of the thin device's logical address space. Thus, a specified SLO for a thin device may be used to select a storage tier for initial physical storage allocation to store write data for the thin device. As described herein, each storage tier may have physical storage devices of a particular media type. Additionally, in an embodiment in accordance with techniques herein, each storage tier may include such physical storage devices of a media type or technology (e.g., EFD, FC 10K RPM, FC 15K RPM, SATA 7.2K RPM) configured in a RAID group having an associated RAID protection type or level and configuration. Thus, physical storage location (of a storage tier) such as may be allocated in a multi-tiered storage environment may be characterized as having a first dimension denoting the media type or technology of the PDs in the storage tier and a second dimension denoting the RAID type or level (e.g., RAID-1, RAID-5, RAID-6) and configuration (e.g., of the RAID group such as RAID-5 with 3×1 (3 data drives and 1 parity drive) or 7×1 (7 data drives and 1 parity drive).

As an example of an embodiment illustrating techniques herein, consider an embodiment which supports RAID-1, RAID-5 (3×1), and RAID-6 groups and where the PDs in a configured RAID group may include PDs of any of the following media types or technologies: EFD, FC 15K RPM rotating disk drives FC 10K RPM rotating disk drives, and SATA 7.2 K RPM rotating disk drives. In such an embodiment, each of the possible 4 media types may have an associated expected level of performance such as expected average RT (e.g., that may be determined based on modeling, performance testing, specifications provided by manufacturer or provider of PDs of different RPMs, and the like). The foregoing 4 media types or technologies may have an associated performance ranking, from highest performance ranking to lowest performance ranking, of EFD, FC 15K RPM, FC 10K RPM, SATA 7.2K RPM. Additionally the following may be expected average RTs for each of the media types: EFD=2 ms RT, FC 15K RPM=8-12 ms RT, FC 10K RPM=12-15 ms RT, and SATA 7.2K RPM 20+ms RT. Additionally, each of the possible RAID group types and configurations may an associated ranking, from lowest write penalty cost to highest write penalty cost, of RAID-1, RAID-5 3×1, and RAID-6.

In connection with techniques herein, when initially allocating physical storage for a thin device chunk responsive to a first write to a logical address in that thin device chunk, physical storage may be allocated from a storage tier having an associated media type or technology with an expected level of performance that most closely matches an SLO specified for the thin device.

For example, consider a data storage system for which a customer may purchase one of the following service plan levels: diamond, platinum, gold, silver and bronze, as described elsewhere herein. A first customer may purchase the diamond service plan level with an SLO that is an RTO of 2 ms and the first customer may have an application storing its data on a thin device. When allocating storage responsive to a first write to a logical address of the thin device, physical storage may be allocated from a storage tier having physical storage devices of a media type with an expected RT that is closest to the RTO=2 ms of the SLO for the first customer. Thus storage may be allocated from a storage tier including EFDs (EFD expected RT=2 ms and customer's SLO=2 ms). In an embodiment in which there are multiple RAID group types and configurations of EFDs, selection may be made based on a further ranking of all such EFD configured RAID groups. The ranking of the EFD RAID groups may be based on write penalty, from lowest to highest write penalty. For example, assume there are 3 RAID groups of EFDs ranked from lowest to highest write penalty as follows: a RAID-1 group of EFDs, a RAID-5 group of EFDs and a RAID-6 group of EFDs. Selection of a RAID group for storage allocation for a first write to a logical address of a thin device may be made for the first customer having the diamond service plan from a RAID group of EFDs having available physical storage with the least write penalty. For example, storage may be allocated from the RAID-1 EFD group if it has available capacity. If there is no available capacity in the RAID-1 EFD group (or if there is no RAID-1 EFD group), storage may be allocated from the RAID-5 EFD group if it has available capacity. If there is no available capacity in the RAID-5 EFD group (or if there is no RAID-5 EFD group), storage may be allocated from the RAID-6 EFD group if it has available capacity. If there is no available capacity in the RAID-6 EFD group (or if there is no RAID-6 EFD group), storage may be allocated using another default technique such as described below. In this manner, an embodiment in accordance with techniques herein may allocate new storage in response to a first write to a thin device logical address where the new storage allocation is made from a PD selected in accordance with the SLO associated with the thin device. In such an embodiment, the PD may be of a particular media type or technology having an expected performance, such as RT, that is a closest match of all available media types in the system to the SLO of the thin device. In a similar manner, storage may be allocated for a thin device having an SLO as may be specified based on any one of the different service plan levels in an embodiment in accordance with techniques herein.

Referring to FIG. 17, shown is an example of tables including service plan levels, SLOs and preferred media types that may be used in an embodiment in accordance with techniques herein. In the example 1200, table 1210 may specify service plan levels 1202 and associated SLOs 1204 that may be used in an embodiment in accordance with techniques herein. The table 1210 summarizes the 5 different service plan levels described above from which a customer may select in connection with specifying a service level agreement, for example, with a provider providing data storage in a data storage system. In the table 1210, the diamond service plan has an associated SLO as an RTO of 2 ms. for each LUN of the customer, the platinum service plan has an associated SLO as an RTO of 8 ms. for each LUN of the customer, the gold service plan has an associated SLO as an RTO of 10 ms. for each LUN of the customer, the silver service plan has an associated SLO as an RTO of 15 ms. for each LUN of the customer, and the bronze service plan has an associated SLO as an RTO of 18 ms. for each LUN of the customer. It should be noted that the SLO RTO specified in table 1210 may refer to an average RT for a host I/O.

Table 1220 summarizes expected performance in terms of average RT 1222 for an I/O directed to a PD for the particular media types 1224. Thus, table 1220 generally lists average RTs with respect to backend physical device I/O operations. For example, table 1220 indicates an average RT of 2 ms. for I/Os directed to an EFD, an average RT in the range of 8-12 ms for FC 15K RPM rotating disk drive, an average RT in the range of 14-18 ms for FC 10K RPM rotating disk drive and an average RT of 20 ms or more for a SATA 7.2K RPM rotating disk drive.

Table 1230 lists the plan levels 1232 and the preferred media types 1234 based on the tables 12010 and 1220. The diamond plan has an RTO of 2 ms as in table 1210 which maps to EFD indicated in table 1220 which has a matching RT of 2 ms. The platinum plan has an RTO of 8 ms as in table 1210 which maps to FC 15K RPM drive indicated in table 1220 which has a matching RT in the range of 8-12 ms. The gold plan has an RTO of 10 ms as in table 1210 which maps to FC 15K RPM drive indicated in table 1220 which has a matching RT in the range of 8-12 ms. The silver plan has an RTO of 15 ms as in table 1210 which maps to FC 10K RPM drive indicated in table 1220 which has a matching RT in the range of 14-18 ms. The bronze plan has an RTO of 18 ms as in table 1210 which maps to FC 10K RPM drive indicated in table 1220 which has a matching RT in the range of 14-18 ms.

The foregoing table 1230 may indicate a preferred media type selected for the initial allocation of storage of a thin device chunk in response to a first write to a logical address of the thin device chunk. In an embodiment in which there are multiple RAID group types or protection levels (and associated configurations) for the single preferred media type, one of the multiple RAID group types and associated configuration is selected based on a ranking of such RAID group types from lowest or minimum write penalty (per host I/O) to maximum write penalty (per host I/O), as described above. For example, if there are 3 RAID types or levels as described above for a single media type, the storage may be allocated from one of a RAID-1 group, a RAID-5 group or a RAID-6 group. The foregoing ordering also lists the RAID group type ranking, from minimum to maximum, in terms of write penalty of a single host I/O associated with each type. Thus, the physical storage may be allocated from the RAID group having the RAID type or level and associated configuration which has available storage and the least write penalty.

Criteria for determining a best match between a thin device SLO and one of the media types may vary. For example, one embodiment may select the media type having an expected level of performance, such as expected average RT for I/Os, that is closest to the SLO RT but not less than the SLO RT.

In the event that there is no available storage for allocation based on the preferred media type determined based on SLO, a default technique may be used to select a storage tier from which to allocate the storage for the newly allocated thin device chunk. In one embodiment in accordance with techniques herein, selection may be made from a storage tier based on a predefined ranking determined in accordance with media type or technology and RAID type or protection level such as illustrated in FIG. 18.

Referring to FIG. 18, shown is a table 1300 representing the default allocation ranking preference or ordering from most to least preferred when allocating storage for a first write to a thin device. The ranking may be based on factors including RAID type and configuration and media type or technology. Media type or technology may consider the underlying physical storage media characteristics and expected performance capabilities of such a PD based on, for example, whether the PD is a rotating disk drive or solid state storage, if the PD is a rotating drive, what is the RPM, and the like. Additionally, the foregoing ranking takes into consideration the RAID type and configuration ranking described above based on host I/O write penalties of the different RAID types and configurations. The ranking in table 1300 may take into account factors including physical device performance capability that may vary with media type, RAID type and configuration write penalty, cost per unit of storage (e.g. cost per GB), amount or storage capacity of different media types in the system, and any media wear out. For example, flash-based media experiences wear out based on the number of writes performed. Within a lifetime or usage period, the amount of writes that each type of flash, such as MLC or SLC, may be expected to successfully sustain varies. For example, with SLC, stored one bit of information or data per cell and may be the simplest of all flash types. Due to having only one bit per cell, it may therefore have the longest lasting of the flash types in an embodiment in accordance with techniques herein. In contrast, for example, with MLC, multiple bits of information are stored per cell and wear rate during write operations is greater than with SLC. Thus, during a usage or lifetime period, an SLC device is expected to be able to have a larger number of allowable writes than an MLC device. In this manner, the SLC device may be characterized as a type of flash having a higher write endurance than the MLC device. Furthermore, the SLC device may be generally included in first write endurance classification associated with a first level of write endurance and the MLC device may be generally included in a second write endurance classification associated with a second different level of write endurance. Thus, EFD is a media type that experiences wear out based on the amount of writes to that particular EFD. In this manner, an embodiment in accordance with techniques may consider write endurance or wear out as a factor when determining the ranking of table 1300.

In one embodiment in accordance with techniques herein, the media types may include flash/EFD, FC 15K RPM rotating disk drives, FC 10K RPM rotating disk drives and SATA 7.2 K RPM rotating disk drives. Additionally, the embodiment may include RAID type and configurations of RAID-1, RAID-5, and RAID-6. In table 1300 for such an embodiment, column 1302 lists the different media types and columns 1304, 1306 and 1308 list the 3 different RAID types and configurations. Thus table 1300 has 12 cells or entries each denoting a different combination of media type and RAID type and configuration. The ranking for the 12 entries denoting the different possible combinations of media type and RAID type and configuration may be from 1 to 12 with 1 being the highest ranked or most preferred storage tier from which to initially allocate storage for the thin device chunk, and 12 being the lowest ranked or least preferred storage tier from which to initially allocate storage for the thin device chunk.

Due to factors such as wear out and cost/GB of EFD (e.g., media type), it may be desirable to establish a default ranking as in table 1300 in which EFD is ranked below other media types such as one or more fast rotating disk drives media type of FC 15K and FC 10K RPM disk drives. Additionally, it may be desirable to have the default ranking consider as primary criterion/ia the media type characteristics (e.g., performance, wear out, cost/GB) and as secondary criterion the write performance penalty associated with different RAID types and configurations. Thus, the ranking may use the write performance penalty to rank different RAID types and configurations of the same media type. The default ranking may also place one or more of the slowest performance capability media types, such as SATA 7.2K RPM, in the last or lowest positions in the ranking.

Based on the foregoing, table 1300 lists an example of a default ranking for allocation based on a combination of media type and RAID type and configuration as follows, from highest rank to lowest rank: 1^(st) is FC 15K RPM RAID-1, 2^(nd) is FC 10K RPM, RAID-1, 3^(rd) is EFD RAID-1, 4^(th) is FC 15K RPM RAID-5, 5^(th) is FC 10K RPM, RAID-1, 6th is EFD RAID-5, 7^(th) is FC 15K RPM RAID-6, 8^(th) is FC 10K RPM RAID-6, 9th is EFD RAID-6, 10^(th) is SATA 7.2K RPM RAID-1, 11^(th) is SATA 7.2K RPM RAID-5 and 12^(th) is SATA 7.2K RPM RAID-6.

The ranking table in 1300 may be used by default when there is no SLO associated with a thin LUN when initially allocating storage for a thin LUN chunk responsive to a first write to a logical address of the chunk, or when there is no physical storage available in a storage tier including PDs of the preferred media type having an expected performance that most closely matches the SLO for the thin LUN.

Thus, responsive to first write to a thin LUN chunk, physical storage is allocated for the chunk. In an embodiment in accordance with techniques herein, techniques as described in connection with FIG. 17 may first be performed to allocate storage from a tier including PDs of the preferred media type for the thin LUN if the thin LUN has an associated SLO such as an RTO. If the thin LUN does not have an associated SLO or otherwise if there is no available storage capacity on a PD of the preferred media type for the thin LUN, a default technique may be used, such as allocation from a storage tier based on the default ranking of table 1300.

When allocating storage for first storing data of a first write to a thin LUN chunk using the default ranking of table 1300, storage may be allocated from the tier which matches the highest ranking and which has available storage capacity for allocation. An embodiment may establish allocation limits based on various allocation policies and any allocation may be in accordance with any existing allocation limits. For example, an embodiment may want to keep a minimum threshold percentage or amount of unused storage capacity of one or more media types so that no further storage may be allocated from a media type once that threshold is reached. In this case, when selecting a storage tier for allocation based on either the preferred media type determined using a thin LUN SLO or otherwise using the default table 1300, if a first storage tier of a first media type is at an associated allocation limit, storage may be allocated from a different tier having a different media type. Using the table 1300, storage may be allocated from the tier having available storage capacity and which has the highest ranking in table 1300 based on the combination of media type and RAID type and configuration.

Once storage has been allocated for a chunk of a thin LUN, processing may be performed to gather performance data about the chunk such as related to I/O workload directed to the chunk. In one embodiment as described herein, statistics such as related to I/O workload may be collected per extent based on all the I/O workload of all chunks in that extent. Alternatively, an embodiment may store I/O workload information at smaller or finer levels of granularity such as per sub extent, per chunk, or some other level of suitable granularity.

For purposes of illustration, following paragraphs may refer to one embodiment in accordance with techniques herein where I/O workload information is collected per extent, storage for thin LUNs is allocated per chunk and data movement optimizations may move data portions the size of a single sub extent or per chunk between storage tiers.

Thus, although workload information is tracked at the extent level for each TD extent, more specifically, an embodiment in accordance with techniques herein may track workload information at the extent level for the particular chunks of each TD extent having storage allocated in that extent.

Consider the following to illustrate. For example, consider a first thin device TD1 with a first logical address space where storage is allocated for a first chunk C1 in a first extent E1 of TD1 where E1 has a corresponding first logical address subrange of TD1's first logical address space. C1 may also correspond to a second subrange of logical address(es) within the first logical address subrange. Data for C1 may be stored on a first physical storage portion of a PD where the first physical storage portion is mapped to the second subrange of logical address(es) for C1 of TD1 (e.g., such as via an allocation map as described above and illustrated in FIG. 16B). Assume, currently, that C1 is the only chunk of E1 for which physical storage has been allocated (e.g., storage has not been allocated for any other chunk in E1 of TD1's logical address space so that no other chunk in E1 is mapped to physical storage per TD1's allocation map). In this case, the workload information tracked for E1 of TD1 includes only information for C1. At a later point in time, assume a second chunk C2 within E1 of TD1 has physical storage allocated so that both C1 and C2 of E1 of TD1 now have physical storage allocated. Subsequent to this later point in time, the workload information for E1 of TD1 may reflect I/Os directed collectively to both C1 and C2.

Thus, an embodiment may track the I/O workload at an extent-level/per extent where each such extent corresponds to a subrange of logical address space of a single TD(thin device) based on I/Os that are directed to any logical address in the logical address subrange for that extent.

For a thin LUN chunk, subsequent to the initial allocation of storage and placement of write data in the initially allocated physical storage, processing may be performed in an ongoing manner to periodically assess whether there is a need to relocate or move data portions among storage tiers having different PDs of different media types and associated RAID types and configurations. In one embodiment in accordance with techniques herein, the assessment or determination as to whether a data portion currently stored on a PD of a storage tier should be relocated may be made based on one or more movement criteria including a RAID type and configuration of the storage tier where the data portion is currently stored, a media type of the PDs of the storage tier where the data portion is currently stored, and current I/O workload characteristics of the data portion. The I/O workload characteristics may include a write probability and a current I/O workload density such as based on I/O volume or quantity (e.g., number of I/Os directed to a data portion) per unit of storage (e.g., per GB), or based on I/O throughput or I/O rate such as I/Os per second (IOPS) per unit of storage (e.g., per GB).

As described herein, in one embodiment, the statistics of write probability and I/O workload density characterizing the I/O workload may be collected per extent. In a single extent of a thin LUN, not all chunks in the extent may be currently allocated. In such an embodiment, the I/O workload density for the extent may be a ratio of the IOPS directed to any logical address in the extent to the size or storage capacity of the allocated chunks. More formally, I/O workload density, also referred to herein as I/O density, for an extent based on IOPS may be represented as: I/O density=IOPS/total capacity of allocated chunks  EQUATION 1 wherein

I/O density is the calculated I/O workload density for the extent;

IOPS represents the I/O rate, such as I/Os per second, directed to any logical address of thin device range associated with the extent; and

total capacity of allocated chunks represents the size or total amount of allocated storage for allocated chunks in the extent. For example, if the extent includes N chunks and only 2 are allocated, the total capacity of allocated chunks may be expressed as the mathematical product of 2*size of one chunk.

Since the size of read and write I/Os may vary, the write probability may account for both the number or rate of reads and writes as well as the average size of read I/Os and average size of write I/Os. The write probability for a data portion, such as an extent, is the probability of doing a write based on the following for host or front end I/Os:

$\begin{matrix} {{{Write}\mspace{14mu}{probability}} = \frac{{Total}\mspace{14mu}{data}\mspace{14mu}{written}}{\left( {{{Total}\mspace{14mu}{data}\mspace{14mu}{read}} + {{Total}\mspace{14mu}{data}\mspace{14mu}{written}}} \right)}} & {{EQUATION}\mspace{14mu} 2} \end{matrix}$ where

Total data written is the total quantity or amount of data written; and

Total data read is the total quantity or amount of data written.

The write probability determined using EQUATION 2 is a value between 0 and 100%, inclusively.

The Total data written may be calculated as in EQUATION 3 below: Total data written=write rate (e.g., write I/Os per second)*average size of write The Total data read may be calculated as in EQUATION 4 below: Total data read=read rate (e.g., read I/Os per second)*average size of read

In one embodiment, for an extent having one or more chunks of storage thereof allocated, processing may be performed to select a preferred media type for the extent based on the extent's I/O density such as may be determined using EQUATION 1. For the extent, a selection of a preferred RAID type and configuration may be made from those currently configured in an embodiment based on the extent's write density as may be determined using EQUATION 2. A preferred storage tier may be determined as one having PDs of the preferred media type and one having a preferred RAID type and configuration. Further processing may then be performed to move one or more chunks of the extent to the preferred storage tier (if such one or more chunks are not already in PDs of the preferred storage tier. This is described in more detail below.

Generally, the higher performance media types may be preferred for storing data having the highest I/O workload such as may be expressed as having the highest I/O density in an embodiment in accordance with techniques herein. As an alternative, an embodiment may use I/O rate for a data portion, such as an extent, to denote the workload directed to the data portion. As yet another alternative, an embodiment may use another suitable metric to denote the I/O workload of a data portion, such as an extent. Thus, for example, consider an embodiment as described above with 4 media types as in FIG. 18 having an associated performance ranking from highest to lowest of EFD, FC 15 RPM K, FC 10K RPM and SATA 7.2K RPM. Data portions may be preferred for different media types depending on the I/O workload of each of the different data portions, such as each extent. The data portions having the highest I/O workload (“hottest”) of all existing data portions may be stored in the highest performance media type such as EFD. Data portions having lower I/O workloads may accordingly be preferred for lower ranked performance storage. In an embodiment using the I/O density as in EQUATION 1, those data portions having the highest I/O density may be preferred for the highest performance ranked media type.

Furthermore, different RAID type and configurations may be preferred for different read/write mixtures or, more generally, depending on whether the data portion has a read heavy I/O workload (e.g., more reads than writes) or write heavy I/O workload (e.g., more writes than reads). RAID-1 groups may be preferred for write heavy workload and RAID-6 groups may be preferred for read heavy workloads based on the relative write performance penalties as described elsewhere herein for different RAID types and configurations. In one embodiment in accordance with techniques herein, whether workload of a data portion, such as an extent, is write heavy may be expressed using the write probability as may be determined using EQUATION 2 above. In other words, the higher the write probability of an extent as may be determined using EQUATION 2, the greater the write workload or higher the mixture of writes vs. reads for the extent. Thus, in an embodiment in accordance with techniques herein, a preferred RAID type and configuration for a data portion, such as an extent, may be determined based on the write probability of the data portion. Data portions having the highest write probability may be stored in storage tiers having a RAID-1 type and configuration. In contrast, data portions having the lowest write probability (thereby indicating the data portions as the most read heavy) may be stored in storage tiers having a RAID-6 type and configuration.

Referring to FIG. 19, shown is an example illustrating I/O workload characteristics of varying values of I/O density and write probability which may be preferred for different storage tiers having PDs of a particular media type configured into RAID group(s) having a particular RAID-type and configuration. An I/O workload may have a write probability that ranges from all writes or write probability of 100% to all reads or read probability of 100%. The quarter pie graph of 1800 is generally divided into 3 “pie slice” partitions based on radial lines V1 and V2 drawn from the center point 0. In this example, there are 3 RAID group types and configurations so the graph 1800 may be divided into 3 partitions for the number of RAID group types and configurations. In one embodiment, these 3 partitions may be approximately equal each denoting approximately a same amount or portion size of the write probability range 0-100%. In one embodiment, the partition associated with RAID-1 is denoted by portions X1, X4, X7 and X10, the partition associated with RAID-5 is denoted by portions X2, X5, X8 and X11 and the partition associated with RAID-6 is denoted by X3, X6, X9 and X12. Generally, the graph may be divided into N partitions where N denotes the number of different RAID types and configurations in an embodiment.

Additionally, the quarter pie graph is generally divided into 4 arc partitions or circumferential bands partitioned by arcs B1 1820 a, B2 1802 b and B3 1802 c. In this example, there are 4 media types so the graph 1800 may be divided into 4 arc partitions based on arcs B1, B2, and B3. Generally, the graph may be divided into M arc partitions where M denotes the number of different media types in an embodiment. In one embodiment, the arc partition associated with SATA 7.2K RPM is denoted by portions X10, X11 and X12, the arc partition associated with FC 10K RPM is denoted by portions X7, X8 and X9, the arc partition associated with FC 15K RPM is denoted by portions X4, X5 and X6, and the arc partition associated with EFD is denoted by X1, X2 and X3.

Each of the arcs or curves 1802 a-c may generally represent read write mixtures or read/write ratios of I/O workloads ranging from a first mixture or ratio denoted by 1102 to a second mixture or ratio denoting by 1104. In an embodiment described herein using the write probability metric of EQUATION 2, each of the arcs or curves 1802 a-c may represent write probabilities of I/O workloads ranging from a 0% write probability (e.g., all read workload) denoted by 1102 to a 100% write probability (e.g., all writes workload) denoted by 1104. As illustrated, each point at which the X axis 1102 intersects one of the curves 1802 a-c may denote a point on the intersecting curve for 0% write probability. Each point at which the Y axis 1104 intersects one of the curves 1802 a-c may denote a point on the intersecting curve for 100% write probability. Points on the curves 1802 a-c between 1102 and 1104 may represent a write probability of a workload between 0 and 100%. In one embodiment, line V2 may denote approximately 33% write probability and line V1 may denote approximately 67% write probability. It should be noted that the particular boundaries or partitioning of the full range of write probabilities among the three pie slice partitions associated with the tree RAID types of RAID-1, RAID-5 and RAID-6 may vary with embodiment. For example, some embodiments may overlap the write probability boundaries associated with two or more adjacently ranked RAID groups. As illustrated, the highest the write probability space (X1, X4, X7 and X10) is mapped to the RAID-1 type and the lowest write probability space (X3, X6, X9 and X12) is mapped to the RAID-6 type. Additionally, although the example 1800 shows the range of write probabilities as being partitioned in approximately equal parts or pie slices between the different RAID types and configurations, an embodiment may map any suitable portion of the range of write probabilities to each RAID type and configuration.

Generally, movement along a radial line drawn from point 0 may denote an I/O density. As the I/O density increases, the distance from the point 0 increases. In one embodiment, the radial distance of a line drawn from the center point 0 may be associated with a range of I/O densities. Each such radial line drawn from the center point 0, such as V1, V2, 1102 and 1104, may be divided into subranges where each subrange of I/O densities may be mapped or associated with a particular preferred media type. For example, I/O densities in the subrange from 0-B1 may be preferred for SATA 7.2K RPM, I/O densities in the subrange B1-B2 may be preferred for FC 10K RPM, I/O densities in the subrange B2-B3 may be preferred for FC 15K RPM, and I/O densities greater than B3 may be preferred for EFD. Values selected for B1, N2 and B3 may generally be any suitable boundary values. In one embodiment in accordance with techniques herein, the I/O density range may be divided into 4 non-overlapping contiguous subranges which may or may not be the same size. The size of each subrange may vary, for example, with the storage capacity of each media type.

In some embodiments in accordance with techniques herein, the representation of 1800 may logically represent a preferred matching of I/O workload characteristics based on write probability and I/O density (e.g., based on the amount, volume or rate of I/Os) to storage tier characteristics of media type and RAID type and configuration. Such a representation 1800 is consistent with description elsewhere herein based on order of priority, preference, or bias for storing data having an I/O workload that is predominantly reads (e.g., low write probability) in RAID-6 groups and predominantly writes (e.g., high write probability) in RAID-1 groups. Similarly, the representation 1800 indicates the priority, preference or bias of storing data with a large or heavy I/O workload (e.g., high I/O density) in higher performance media types and a low I/O workload (e.g., low I/O density) in lower performance media types. In such an embodiment, those data portions having the highest write probability may be stored in those storage tiers preferred or most suitable for writes such as those having RAID-1 configuration, and those data portions having the lowest write probability may be stored in those storage tiers preferred or most suitable for reads such as those having RAID-6 configuration. In such an embodiment, those data portions having the highest or heaviest I/O workload may be stored in those storage tiers preferred or most suitable for a heavy workload such as those having EFD media type, and those data portions having the lowest I/O workload may be stored in those storage tiers preferred or most suitable for a low workload such as those having the SATA 7.2K RPM media type.

The example 1800 represents a partitioning of the vector space denoted by the combination of I/O density values and write probability values into 12 partitions. Each of the 12 partitions represents one of the twelve possible combinations of media type and RAID type and configuration in an embodiment. Each of the 12 partitions may be associated with a particular subrange of possible I/O density values and a particular subrange of write probability values used to identify I/O workload characteristics of data portions preferred for the particular combination of media type and RAID type of that partition.

Based on the representation of FIG. 19, a preferred media type and preferred RAID type and configuration may be determined for a data portion having an I/O density and a write probability. For example, if a data portion, such as an extent, has a write probability of 100% and a write density greater than that as denoted by B3, a first storage tier configured using RAID-1 and EFD may be determined as preferred for that data portion. If the data portion is an extent, processing may then include moving one or more chunks of the extent to the first storage tier having EFD PDs configured into RAID-1 groups. In contrast, if a data portion, such as an extent, has a write probability of 10% and a write density greater than that as denoted by B3, a second storage tier configured using RAID-6 and EFD may be determined as preferred for that data portion. If the data portion is an extent, processing may then include moving one or more chunks of the extent to the second storage tier having EFD PDs configured into RAID-6 groups.

Referring to FIG. 20 shown is an example 1850 illustrating how each data portion having an associated write probability and I/O density may be represented by a point in the quarter pie graph. The example 1850 may denote the same quarter pie graph as in FIG. 19 with the particular boundaries omitted for simplicity. For a data portion, the write probability may denote a first position or coordinate on an arc such as 1854, and the I/O density may denote a radial distance from the point P0, such as on Line L1, used as a second position or coordinate. For example, P1 may denote a point for such a data portion whereby P1 may have associated coordinate values that fall into subranges (e.g., mapped to) of one of the 12 portions denoted as X1 to X12 identifying preferred media type and RAID type and configuration for the data portion.

What will now be described are flowcharts summarizing processing steps described above that may be performed in an embodiment in accordance with techniques herein.

Referring to FIG. 21, shown is a first flowchart of processing steps that may be performed in an embodiment in accordance with techniques herein. The flowchart 1400 includes step 1402 where preferred media types for the different SLOs are determined such as described in connection with FIG. 18. Additionally, for each such preferred media type as may be used in connection with initial storage allocation for thin device chunk, a relative ranking of RAID types and configurations may be established ranking the RAID types from least write penalty to highest write penalty. For example, one ranking may be RAID-1 (least write penalty), RAID-5 and RAID-6 (highest write penalty). Additionally, step 1402 may include determining a default allocation ranking for possible combinations of media type and RAID type and configuration such as, for example, the ranking described in connection with FIG. 18. At step 1403 a, an I/O operation directed to a chunk of a thin device may be received. At step 1403 b, a determination is made as to whether the I/O is a read operation. If step 1403 b determines the I/O operation is a read, control proceeds to step 1401 where a determination is made as to whether storage is currently allocated or mapped to the chunk to which the read is directed. If step 1401 evaluates to no, control proceeds to step 1411. In step 1411, one embodiment in accordance with techniques herein may return a zero (0) denoting that no storage is currently allocated. As described herein, storage may be allocated for a chunk the first time there is a write to a logical address associated with the chunk. In this case where step 1411 is performed, there has been a read to a logical address prior to storage being allocated for the logical address. Thus, step 1411 returns a zero to denote this condition. If step 1401 evaluates to yes, control proceeds to step 1403 c where workload information for the extent including the chunk is updated. Otherwise, if step 1403 b evaluates to no, control proceeds to step 1404 where it is determined that the I/O is a write received for a thin device. At step 1406, the write data is stored in cache and an acknowledgement regarding the successful completion of the write may be returned in step 1407. In step 1408, a determination is made as to whether this write operation is the first write to the chunk whereby no physical storage is currently mapped to the logical addresses of the thin device's address space corresponding to the chunk. If step 1408 evaluates to yes indicating this is the first write to the chunk, first write processing is performed in step 1412. If step 1408 evaluates to no, subsequent write processing is performed in step 1410.

Referring to FIG. 22, shown is a second flowchart of processing steps that may be performed in an embodiment in accordance with techniques herein. The flowchart 1500 provides additional details regarding step 1412. At step 1501 a, a determination is made as to whether the thin device LUN to which the write is directed is associated with an SLO, such as an RTO. If step 1501 a evaluates to no, control proceeds to step 1502 where storage for the chunk may be allocated from a storage tier having characteristics based on the default allocation ranking such as, for example, based on the ranking of FIG. 18. From step 1502, control proceeds to step 1504.

If step 1501 a evaluates to yes, control proceeds to step 1501 b where a determination is made as to whether there is storage available in a tier having the preferred media type for the LUN based on the SLO. If step 1501 b evaluates to no, control proceeds to step 1502. If step 1501 b evaluates to yes, control proceeds to step 1503 to allocate storage from a tier having the preferred media type determined based on the SLO for the LUN. If there are multiple tiers having PDs of the preferred media type, one of the multiple tiers is selected with the RAID type and configuration having the least write penalty of all such multiple tiers.

At step 1504, the allocated storage is mapped to the logical addresses of the chunk. At step 1506, the write data is destaged from cache to the newly allocated storage (as allocated in step 1504). At step 1508, workload information for the extent including the chunk is updated to reflect the write operation just received.

Referring to FIG. 23, shown is a third flowchart of processing steps that may be performed in an embodiment in accordance with techniques herein. The flowchart 1600 provides additional details regarding step 1410. At step 1602, the physical storage location is determined that is mapped to the chunk including the logical address to which the write operation is directed. In step 1602, the write data is destaged from cache to the physical storage location determined in step 1602. At step 1606, I/O workload information for the extent including the logical address to which the write operation is directed (e.g. including the chunk to which write is directed) is updated to reflect the write operation.

Referring to FIG. 24, shown is a fourth flowchart of processing steps that may be performed in an embodiment in accordance with techniques herein. The flowchart 1700 may be performed in an ongoing manner such as periodically at predetermined time interval occurrences to evaluate. For example, the flowchart 1700 may be performed to periodically assess data portions, such as extents, and determine if any data movement optimization is needed to relocate data from its current storage tier to another target tier determined as more suitable or preferred based on the write probability and I/O density of the data portion. FIG. 24 processing may also be performed at other time such as, for example, responsive to consuming more than a threshold amount of a particular media type, responsive to a particular SLO for a thin LUN not being met, and the like.

At step 1702, an extent is selected for which processing is to be performed and the preferred media type and preferred RAID type and configuration for the extent may be determined. As described herein, the preferred media type and preferred RAID type and configuration for the extent may be determined based on the I/O density and write probability for the extent such as described in connection with FIG. 19. At step 1704, one or more chunks of the extent having their data stored in a storage tier that does not have the preferred media type and preferred RAID type are determined. Each of the one or more chunks are thereby determined in step 1704 as being stored in a current storage tier that may be characterized as unsuitable or not preferred for the chunk based on the I/O density and write probability of the extent including the chunk. At step 1706, a determination is made as to whether step 1704 identified any chunk(s) currently stored in a storage tier having a media type and RAID type and configuration that does not match those preferred as determined in step 1702. If step 1706 evaluates to no whereby no chunk is identified in step 1704, control proceeds to step 1710 to process and select a next extent in step 1702. If step 1706 evaluates to yes, for each of the one or more chunks identified, processing may be performed to relocate the chunk to a storage tier having the preferred media type and preferred RAID type and configuration. Relocating a chunk from a current to a target storage tier may include allocating storage for the chunk in the target storage tier and mapping the newly allocated storage to the chunk corresponding logical address subrange of the thin LUN including the chunk. From step 1708, control proceeds to step 1710.

It should be noted that the number of chunks moved or relocated as a unit in step 1708 may vary with the level of data movement granularity used in an embodiment. For example, one embodiment in accordance with techniques herein may move a group of chunks as a unit such as in an embodiment having a subextent as the data movement granularity. In another embodiment in accordance with techniques herein, individual or single chunks may be moved or relocated having a chunk as the data movement granularity.

It should also be noted that processing may be performed responsive to consuming more than a threshold amount of capacity of one or more storage tiers having one or more particular characteristics such as a particular RAID-type and/or media type. Such processing may be performed to evict or relocate data portions currently stored therein to make additional storage capacity available in storage tiers of a particular media type and/or particular RAID-type and configuration. Such relocation may consider both RAID type and media type as described above, such as in connection with FIG. 24 processing. As another option, such processing may consider just one of the foregoing when determining what data portions to evict or relocate. For example, one embodiment in accordance with techniques herein may determine that there is an insufficient amount of available storage in storage tiers having RAID-1 configuration. In such an embodiment, selection of data portions for eviction or movement from a RAID-1 tier may be those data portions having a low write probability. Similarly, if it is determined that there is an insufficient amount of available storage in storage tiers having RAID-6 configuration. In such an embodiment, selection of data portions for eviction or movement from a RAID-6 tier may be those data portions having a high write probability (e.g., more suited for RAID-1). The target storage tier to which such evicted data portions may be moved may have a media type that is the same or higher in the performance ranking of media types. The techniques herein may be performed by executing code which is stored on any one or more different forms of computer-readable media. Computer-readable media may include different forms of volatile (e.g., RAM) and non-volatile (e.g., ROM, flash memory, magnetic or optical disks, or tape) storage which may be removable or non-removable.

While the invention has been disclosed in connection with preferred embodiments shown and described in detail, their modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention should be limited only by the following claims. 

What is claimed is:
 1. A method of storing data comprising: receiving a write operation directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address, said logical device having a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; selecting a storage tier from a plurality of storage tiers from which to allocate storage for storing write data of the write operation, wherein said selecting is performed in accordance with determining a match between an expected level of performance of said storage tier of physical storage devices having a same physical device type and said performance goal of the logical device as denoted by the service level objective, wherein said selecting includes: determining whether the logical device has any associated service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; and responsive to determining that the logical device does not have any associated service level objective, using a default ranking of the plurality of storage tiers to select the storage tier as a highest ranked one of the plurality of storage tiers having available capacity, wherein said plurality of tiers are configured into RAID groups having write performance penalties, wherein said default ranking of the plurality of storage tiers is ranked in accordance with one or more primary criteria including media type characteristics and one or more secondary criteria including the write performance penalties associated with different RAID types and configurations, wherein each of the different RAID types with an associated configuration has an associated one of the write performance penalties denoting a number of additional back-end I/O operations incurred when issuing a single write operation that stores data in a RAID group configured with said each RAID type and associated configuration; allocating first physical storage from the storage tier; mapping a logical address subrange of the logical device to the first physical storage; and storing the write data in the first physical storage at a physical storage location mapped to the target logical address.
 2. The method of claim 1, wherein each of the plurality of storage tiers has characteristics denoting a media type of physical storage devices of said each tier and denoting a RAID type and configuration of physical storage devices.
 3. The method of claim 2, wherein the media type associated with said each storage tier denotes an expected level of performance with respect to I/O operations directed to said each tier.
 4. The method of claim 1, wherein the performance goal of the service level objective and the expected level of performance of said storage tier are response times.
 5. The method of claim 2, wherein said plurality of storage tiers includes a first storage tier having first characteristics identifying a media type with an expected level of performance matching the performance goal of the service level objective and identifying a first RAID type and configuration, and a second storage tier having second characteristics identifying a media type with an expected level of performance matching the performance goal of the service level objective and identifying a second RAID type and configuration, and wherein said selecting further comprises: determining a first write penalty associated with the first RAID type and configuration; determining a second write penalty associated with the second RAID type and configuration; and selecting the first storage tier rather than the second storage tier from which to allocate storage for storing the write data if the first write penalty is less than said second write penalty, otherwise selecting the second storage tier rather than the first storage tier.
 6. The method of claim 1, wherein the storage tier is characterized by a first media type denoting that the storage tier includes physical devices of the first media type and wherein the storage tier is characterized by a first RAID type and configuration denoting that physical devices of the storage tier are configured into one or more RAID groups of the first RAID type and configuration, and the method further comprising: collecting I/O workload information for a data portion including the target logical address and the logical address subrange of the logical device; determining, based on the I/O workload information, a preferred media type and a preferred RAID type and configuration for the data portion; determining, for first data of the data portion currently stored in the storage tier, whether said first RAID type and configuration matches the preferred RAID type and configuration, and whether said first media type matches said preferred media type; responsive to determining that any of said first RAID type and configuration does not match the preferred RAID type and configuration, and said first media type does not match said preferred media type, selecting the first data of the data portion to be moved from the storage tier to a target storage tier.
 7. The method of claim 6, wherein the target storage tier has said preferred RAID type and configuration and said preferred media type.
 8. The method of claim 6, wherein the I/O workload information includes a write probability for said data portion.
 9. The method of claim 6, wherein the I/O workload information includes an I/O density for the data portion.
 10. The method of claim 6, wherein the I/O workload information includes a first metric based on I/O throughput for the data portion.
 11. The method of claim 6, wherein the I/O workload information includes a second metric based on an amount of data read in connection with I/Os directed to the data portion and based on an amount of data written in connection with I/Os directed to the data portion.
 12. A system comprising: a processor; and a memory comprising code stored therein that, when executed, performs a method comprising: receiving a write operation directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address, said logical device having a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; selecting a storage tier from a plurality of storage tiers from which to allocate storage for storing write data of the write operation, wherein said selecting is performed in accordance with determining a match between an expected level of performance of said storage tier of physical storage devices having a same physical device type and said performance goal of the logical device as denoted by the service level objective, wherein said selecting includes: determining whether the logical device has any associated service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; and responsive to determining that the logical device does not have any associated service level objective, using a default ranking of the plurality of storage tiers to select the storage tier as a highest ranked one of the plurality of storage tiers having available capacity, wherein said plurality of tiers are configured into RAID groups having write performance penalties, wherein said default ranking of the plurality of storage tiers is ranked in accordance with one or more primary criteria including media type characteristics and one or more secondary criteria including the write performance penalties associated with different RAID types and configurations, wherein each of the different RAID types with an associated configuration has an associated one of the write performance penalties denoting a number of additional back-end I/O operations incurred when issuing a single write operation that stores data in a RAID group configured with said each RAID type and associated configuration; allocating first physical storage from the storage tier; mapping a logical address subrange of the logical device to the first physical storage; and storing the write data in the first physical storage at a physical storage location mapped to the target logical address.
 13. A non-transitory computer readable medium comprising code stored thereon that, when executed, performs a method that stores data comprising: receiving a write operation directed to a target logical address of a logical device where physical storage has not been allocated for the target logical address, said logical device having a service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; selecting a storage tier from a plurality of storage tiers from which to allocate storage for storing write data of the write operation, wherein said selecting is performed in accordance with determining a match between an expected level of performance of said storage tier of physical storage devices having a same physical device type and said performance goal of the logical device as denoted by the service level objective, wherein said selecting includes: determining whether the logical device has any associated service level objective denoting a performance goal to be maintained with respect to I/O operations for the logical device; and responsive to determining that the logical device does not have any associated service level objective, using a default ranking of the plurality of storage tiers to select the storage tier as a highest ranked one of the plurality of storage tiers having available capacity, wherein said plurality of tiers are configured into RAID groups having write performance penalties, wherein said default ranking of the plurality of storage tiers is ranked in accordance with one or more primary criteria including media type characteristics and one or more secondary criteria including the write performance penalties associated with different RAID types and configurations, wherein each of the different RAID types with an associated configuration has an associated one of the write performance penalties denoting a number of additional back-end I/O operations incurred when issuing a single write operation that stores data in a RAID group configured with said each RAID type and associated configuration; allocating first physical storage from the storage tier; mapping a logical address subrange of the logical device to the first physical storage; and storing the write data in the first physical storage at a physical storage location mapped to the target logical address.
 14. The non-transitory computer readable medium of claim 13, wherein each of the plurality of storage tiers has characteristics denoting a media type of physical storage devices of said each tier and denoting a RAID type and configuration of physical storage devices.
 15. The non-transitory computer readable medium of claim 14, wherein the media type associated with said each storage tier denotes an expected level of performance with respect to I/O operations directed to said each tier.
 16. The non-transitory computer readable medium of claim 13, wherein the performance goal of the service level objective and the expected level of performance of said storage tier are response times.
 17. The non-transitory computer readable medium of claim 14, wherein said plurality of storage tiers includes a first storage tier having first characteristics identifying a media type with an expected level of performance matching the performance goal of the service level objective and identifying a first RAID type and configuration, and a second storage tier having second characteristics identifying a media type with an expected level of performance matching the performance goal of the service level objective and identifying a second RAID type and configuration, and wherein said selecting further comprises: determining a first write penalty associated with the first RAID type and configuration; determining a second write penalty associated with the second RAID type and configuration; and selecting the first storage tier rather than the second storage tier from which to allocate storage for storing the write data if the first write penalty is less than said second write penalty, otherwise selecting the second storage tier rather than the first storage tier.
 18. The non-transitory computer readable medium of claim 13, wherein the storage tier is characterized by a first media type denoting that the storage tier includes physical devices of the first media type and wherein the storage tier is characterized by a first RAID type and configuration denoting that physical devices of the storage tier are configured into one or more RAID groups of the first RAID type and configuration, and the method further comprising: collecting I/O workload information for a data portion including the target logical address and the logical address subrange of the logical device; determining, based on the I/O workload information, a preferred media type and a preferred RAID type and configuration for the data portion; determining, for first data of the data portion stored in the storage tier, whether said first RAID type and configuration matches the preferred RAID type and configuration, and whether said first media type matches said preferred media type; responsive to determining that any of said first RAID type and configuration does not match the preferred RAID type and configuration, and said first media type does not match said preferred media type, selecting the first data of the data portion to be moved from the storage tier to a target storage tier.
 19. The non-transitory computer readable medium of claim 18, wherein the target storage tier has said preferred RAID type and configuration and said preferred media type.
 20. The non-transitory computer readable medium of claim 18, wherein the I/O workload information includes a write probability for said data portion and an I/O density for the data portion. 